Registrant’s telephone number, including area code: (301) 984-9400

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    YES  x    NO  ¨

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.    YES  ¨    NO  x

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or such shorter period that the registrant was required to file such reports) and (2) has been subject to such filing requirements for the past ninety (90) days.    YES  x    NO  ¨

Indicate by checkmark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    YES  ¨x    NO  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of the registrant’sregistrant's knowledge in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.    x

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting company. See definition of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer  x            Accelerated filer  ¨            Non-accelerated filer  ¨            Smaller reporting company  ¨

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act).    YES  ¨    NO  x

As of June 30, 2009,2010, the aggregate market value of such shares held by non-affiliates of the registrant was approximately $1,293,242,069$1,710,524,544 (based on the closing price of the stock on June 30, 2009)2010).

As of February 25, 2010, 59,818,31818, 2011, 65,895,876 common shares were outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of our definitive Proxy Statement relating to the 20102011 Annual Meeting of Shareholders, to be filed with the Securities and Exchange Commission, are incorporated by reference in Part III, Items 10-14 of this Annual Report on Form 10-K as indicated herein.

WASHINGTON REAL ESTATE INVESTMENT TRUST

20092010 FORM 10-K ANNUAL REPORT

INDEX

PART I

ITEM 1:  BUSINESS

WRIT Overview

Washington Real Estate Investment Trust (“we” or “WRIT”) is a self-administered, self-managed, equity real estate investment trust (“REIT”) successor to a trust organized in 1960. Our business consists of the ownership and operation of income-producing real property in the greater Washington metro region. We own a diversified portfolio of office buildings, medical office buildings, industrial/flex properties, multifamily buildings and retail centers.

We believe that we qualify as a REIT under Sections 856-860 of the Internal Revenue Code and intend to continue to qualify as such. To maintain our status as a REIT, we are required to distribute 90% of our ordinary taxable income to our shareholders. When selling properties, we have the option of (a) reinvesting the sales proceeds of properties sold, allowing for a deferral of income taxes on the sale, (b) paying out capital gains to the shareholders with no tax to us or (c) treating the capital gains as having been distributed to our shareholders, paying the tax on the gain deemed distributed and allocating the tax paid as a credit to our shareholders.

Over the last five years, dividends paid per share have been $1.73 for 2009, $1.72 for 2008, $1.68 for 2007, $1.64 for 2006 and $1.60 for 2005.

Our geographic focus is based on two principles:

We consider markets to be local if they can be reached from Washington within two hours by car. While we have historically focused most of our investments in the greater Washington metro region, in order to maximize acquisition opportunities we will consider investments within the two-hour radius described above. We also may consider opportunities to duplicate our Washington-focused approach in other geographic markets which meet the criteria described above.

All of our officers and employees live and work in the greater Washington metro region and all but one of our officers have over 20 years of experience in this region.

This section includes or refers to certain forward-looking statements. You should refer toOver the explanation of the qualificationslast five years, dividends paid per share have been $1.73125 for 2010, $1.73 for 2009, $1.72 for 2008, $1.68 for 2007 and limitations on such forward-looking statements beginning on page 50.$1.64 for 2006.

The Greater Washington Metro Area Economy

In 2009, the national economic recession negatively affected2010, the Washington metro region, evidenced by negativeregion’s economy improved significantly from the prior year, with positive job growth and a decreasean increase in gross regional product (“GRP”). Current estimates by Delta Associates / Transwestern Commercial Services (“Delta”), a national full service real estate firm that provides market research and evaluation services for commercial property, indicate that the Washington metro region lost 24,000gained 20,000 – 25,000 jobs in twelve months ending October2010, compared to a loss of almost 53,000 in 2009. The region’s unemployment rate was 6.2%6.0% at October 2009, upNovember 2010, down from 4.1%6.1% in the prior year. However, it stillThe region’s unemployment rate remains the lowest rate among all of the nation’s largest metro areas. In addition, the region’s unemployment rateareas, and is well below the national average of 10.0% in November 2009.9.8%. The federal government education/health and professional/business services sectors experienced positive job growth, whileremains the other sectors recorded job losses. The Center for Regional Analysis at George Mason University (“CRA”) estimates that the Washington area’s GRP decreased by 0.5% in 2009, which is less severe than the estimated national decline of 2.5%. Approximately one-thirdregion’s most important industry, providing approximately one third of the area’s GRP was generated by the federal government.region’s GRP.

CRADelta expects growth in the Washington metro region to be slowaccelerate from recovery to expansion in 2011, albeit slower than in prior recoveries due to a more cautious business community as the region and the nation recoverwell as more austere spending policies from the severe economic conditions.federal government. According to CRA,Delta, the Washington Leading Index, which forecasts area economic performance over the next 18 months, is 107.0,107.2, as of September 2009,2010, which is above the 20-year average of 102.6. CRADelta also forecasts GRP for the Washington metro region to increase by 2.7%3.3% - 3.6% in 2010. This compares to a national GRP projection of 2.5%3.0% - 3.5%. CRADelta forecasts job growth in the region to increase in 20102011 and 2011,2012, adding 24,90048,100 and 34,90044,000 new jobs, respectively, compared to the 15-year20-year annual average of 52,100.37,000.

Greater Washington Metro Region Real Estate Markets

The Association of Foreign Investors in Real Estate (“AFIRE”) has publicized that it now considers Washington DC as the top U.S. city for real estate investment. The area’smetro region’s economy has translated into strongerimproving relative real estate market performance in each of our segments, compared to other national metropolitan regions, as reported by Delta. Despite our region’s strength in comparison to other metropolitan regions, we believe the potential exists in the current economic environment for continued downward pressure on rents in 2010. Market statistics and information from Delta are set forth below:

Office and Medical Office Sectors

Retail Sector

Multifamily Sector

Industrial/Flex Sector

Our Portfolio

As of December 31, 2009,2010, we owned a diversified portfolio of 9085 properties, consistingtotaling approximately 10.7 million square feet of 27commercial space and 2,540 residential units, and land held for development. These 85 properties consist of 25 office properties, 18 medical office properties, 1415 retail centers, 11 multifamily properties 20and 16 industrial/flex properties and land for development.properties. Our principal objective is to invest in high quality properties in prime locations, then proactively manage, lease and direct ongoing capital improvement programs to improve their economic performance. The percentage of total real estate rental revenue by property group for 2010, 2009 2008 and 2007,2008, and the percent leased, calculated as the percentage of physical net rentable area leased, as of December 31, 2009,2010, were as follows:

On a combined basis, our commercial portfolio (i.e., our office, medical office, retail and industrial properties, but not our multifamily properties) was 88% leased at December 31, 2010, 90% leased at December 31, 2009 94%and 95% leased at December 31, 2008 and 97% leased at December 31, 2007.2008.

The commercial lease expirations for the next five years are as follows:

Total real estate rental revenue from continuing operations was $306.9$298.0 million for 2010, $298.2 million for 2009 $278.7and $268.7 million for 2008 and $248.9 million for 2007.2008. During the three year period ended December 31, 2009,2010, we acquired fourthree office buildings, sixtwo medical office buildings, one multifamily building, one retail center and twoone industrial/flex properties.property. We also placed into service from development one office building and twoone multifamily buildings.building. During that same time frame, we sold threefive office buildings, one multifamily building and foureight industrial/flex properties. These acquisitions and dispositions were the primary reason for the shifting of each group’s percentage of total real estate rental revenue reflected above.

No single tenant accounted for more than 3.2%3.3% of real estate rental revenue in 2009, 3.5%2010, 3.3% of revenue in 20082009 and 3.6% of revenue in 2007.2008. All federal government tenants in the aggregate accounted for approximately 2.0%2.6% of our 20092010 total revenue. Federal government tenants include the Department of Defense, U.S. Patent and Trademark Office, Federal Bureau of Investigation, Office of Personnel Management, Secret Service, Federal Aviation Administration, NASA and the National Institutes of Health. Our larger non-federal governmentten largest tenants, include the World Bank, The Advisory Board Company, INOVA Health System, IBM Corporation, Patton Boggs LLP, Sunrise Senior Living, Inc., URS Corporation, Lafarge North America, Inc., and Children’s National Medical Center.in terms of aggregate occupied square feet, are as follows:

5.

Patton Boggs LLP;

We expect to continue investing in additional income-producing properties. We invest in properties which we believe will increase in income and value. Our properties typically compete for tenants with other properties throughout the respective areas in which they are located on the basis of location, quality and rental rates.

In prior years, we have been engaged in significant ground-up development in order to further strengthen our portfolio with long-term growth prospects. In 2007 and 2008, we completed construction on three ground-up development projects. The first was Bennett Park, a 224-unit multifamily property located in Arlington, VA, with the majority of

units delivered by the end of 2007. The second development project was The Clayborne Apartments, a 74-unit multifamily property located in Alexandria, VA. All of the units at Clayborne were delivered during the first quarter of 2008. Bennett Park and Clayborne were 98% and 95% leased, respectively, at December 31, 2009. The third development project was Dulles Station, a Class A office property located in Herndon, VA. Dulles Station is entitled for two office buildings totaling 540,000 square feet. The first 180,000 square foot office building was completed in the third quarter 2007, and was 91% leased at December 31, 2009. Construction of the 360,000 square foot second building remains in the planning phase.

We make capital improvements on an ongoing basis to our properties for the purpose of maintaining and increasing their value and income. Major improvements and/or renovations to the properties in 2010, 2009, 2008, and 20072008 are discussed in Item 7, Management’s Discussion and Analysis of Financial Condition and Results of Operations, under the heading “Capital Improvements and Development Costs.”

Further description of the property groups is contained in Item 2, Properties and in Schedule III. Reference is also made to Item 7, Management’s Discussion and Analysis of Financial Condition and Results of Operations.

On February 25, 2010,18, 2011, we had 301293 employees including 226213 persons engaged in property management functions and 7580 persons engaged in corporate, financial, leasing, asset management and other functions.

REIT Tax Status

We believe that we qualify as a REIT under Sections 856-860 of the Internal Revenue Code and intend to continue to qualify as such. To maintain our status as a REIT, we are required to distribute 90% of our ordinary taxable income to our shareholders. When selling properties, we have the option of (a) reinvesting the sales proceeds of properties sold, allowing for a deferral of income taxes on the sale, (b) paying out capital gains to the shareholders with no tax to us or (c) treating the capital gains as having been distributed to our shareholders, paying the tax on the gain deemed distributed and allocating the tax paid as a credit to our shareholders.

Tax Treatment of Recent Disposition Activity

We sold several properties during the three year period ended December 31, 2009. 2010:

All disclosed gains on sale are calculated in accordance with U.S. generally accepted accounting principles (“GAAP”).

In May 2009, we sold a multifamily property, Avondale Apartments, for a gain of $6.7 million. In July 2009, we sold an industrial property, Tech 100 Industrial Park, for a gain of $4.1 million. In July 2009, we sold an office property, Brandywine Center, for a gain of $1.0 million. In November 2009, we sold another industrial property, Crossroads Distribution Center, for a gain of $1.5 million. The capital gains from the sales were paid out to shareholders.

In June 2008, we sold two industrial properties, Sullyfield Center and The Earhart Building, for a gain of $15.3 million. The capital gains from the sales were paid out to shareholders.

In September 2007, we sold two office properties, Maryland Trade Centers I and II, for a gain of $25.0 million. The proceeds from the sales were reinvested in replacement properties.

We distributed all of our 2010, 2009 2008 and 20072008 ordinary taxable income to our shareholders. No provision for income taxes was necessary in 2010, 2009 2008 or 2007.2008.

Availability of Reports

Copies of this Annual Report on Form 10-K, as well as our Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and any amendments to such reports are available, free of charge, on the Internet on our website www.writ.com. All required reports are made available on the website as soon as reasonably practicable after they are electronically filed with or furnished to the Securities and Exchange Commission. The reference to our website address does not constitute incorporation by reference of the information contained in the website and such information should not be considered part of this document.

ITEM 1A: RISK FACTORS

Set forth below are the risks that we believe are material to our shareholders. We refer to the shares of beneficial interest in WRIT as our “common shares,” and the investors who own shares as our “shareholders.” This section includes or refers to certain forward-looking statements. You should refer to the explanation of the qualifications and limitations on such forward-looking statements beginning on page 50.53.

Further disruptionsDisruptions in the financial markets could affect our ability to obtain financing or have other adverse effects on us or the market price of our common shares.

The United States and global equity and credit markets recentlyhave experienced in the recent past significant price volatility and liquidity disruptions which caused the market prices of stocks to fluctuate substantially and the spreads on prospective debt financings to widen considerably. These circumstances significantly negatively impacted liquidity in the financial markets, making terms for certain financings less attractive or unavailable. FurtherAny disruption in the equity and credit markets could negatively impact our ability to access additional financing at reasonable terms or at all. If such further disruption were to occur, in the event of a debt financing, our cost of borrowing in the future would likely be significantly higher than historical levels. As well, in the case of a common equity financing, the disruptions in the

financial markets could have a material adverse effect on the market value of our common shares, potentially requiring us to issue more shares than we would otherwise have issued with a higher market value for our common shares. Further disruptionDisruption in the financial markets also could negatively affect our ability to make acquisitions, undertake new development projects and refinance our debt. As well,In addition, it could also make it more difficult for us to sell properties and could adversely affect the price we receive for properties that we do sell, as prospective buyers experience increased costs of financing and difficulties in obtaining financing.

Further disruptionsDisruptions in the financial markets also could adversely affect many of our tenants and their businesses, including their ability to pay rents when due and renew their leases at rates at least as favorable as their current rates. As well, our ability to attract prospective new tenants in the future could be adversely affected by disruption in the financial markets.

Our performance and value are subject to risks associated with our real estate assets and with the real estate industry.

Our economic performance and the value of our real estate assets are subject to the risk that if our office, medical office, retail, multifamily and industrial properties do not generate revenues sufficient to meet our operating expenses, debt service and capital expenditures, our cash flow and ability to pay distributions to our shareholders will be adversely affected. The following factors, among others, may adversely affect the cash flow generated by our commercial and multifamily properties:

We are dependent upon the economic climate of the Washington metropolitan region.

All of our properties are located in the Washington metropolitan region, which may expose us to a greater amount of market dependent risk than if we were geographically diverse. General economic conditions and local real estate conditions in our geographic region may be dependent upon one or more industries, thus a downturn in one of the industries may have a particularly strong effect. In particular, economic conditions in our market are directly affected by federal government spending in the region. In the event of reduced federal spending or negative economic changes in our region, we may experience a negative impact to our profitability and may be limited in our ability to make distributions to our shareholders.

We may be adversely affected by any significant reductions in federal government spending.

As aREIT operating exclusively in the Washington, D.C. metropolitan area, a significant portion of our properties is occupied by United States Government tenants or tenants that are directly or indirectly serving the United States Government as federal contractors or otherwise. A significant reduction in federal government spending could affect the ability of these tenants to fulfill lease obligations or decrease the likelihood that they will renew their leases with us. Further, economic conditions in the Washington, D.C. metropolitan area are significantly dependent upon the level of federal government spending in the region. In the event of a significant reduction in federal government spending, there could be negative economic changes in our region which could adversely impact the ability of our tenants to perform their financial obligations under our leases or the likelihood of their lease renewal. As a result, if such a reduction in federal government spending were to occur, we could experience an adverse effect on our financial condition, results of operations, cash flows and ability to make distributions to our shareholders.

We face risks associated with property acquisitions.

We intend to continue to acquire properties which would continue to increase our size and could alter our capital structure. Our acquisition activities and results may be exposed to the following risks:

We may acquire properties subject to liabilities and without recourse, or with limited recourse with respect to unknown liabilities. As a result, if liability were asserted against us based upon the acquisition of a property, we may have to pay substantial sums to settle it, which could adversely affect our cash flow. Unknown liabilities with respect to properties acquired might include:

Real estate investments are illiquid, and we may not be able to sell our properties on a timely basis when we determine it is appropriate to do so.

Real estate investments can be difficult to sell and convert to cash quickly, especially if market conditions are not favorable, and we may find that to be the case under the current economic conditions due to limited credit availability for potential buyers. Such illiquidity could limit our ability to quickly change our portfolio of properties in response to changes in economic or other conditions. Moreover, under certain circumstances, the Internal Revenue Code imposes penalties on a REIT that sells property held for less than two years and or sells more than a specified number of properties in a given year. In addition, for properties that we acquire by issuing units in an operating partnership, we may be restricted by agreements with the sellers of the properties for a certain period of time from entering into transactions (such as the sale or refinancing of the acquired property) that will result in a taxable gain to the sellers without the sellers’ consent. Due to these factors, we may be unable to sell a property at an advantageous time.

We face potential difficulties or delays renewing leases or re-leasing space.

FromAs of December 31, 2010, through 2014, leases on our commercial properties will expire on a total of approximately 69% of our leased square footagefrom 2011 through 2015 as of December 31, 2009, with leases on approximately 16% of our leased square footage expiring in 2010, 16% in 2011, 12% in 2012, 14% in 2013 and 11% in 2014. follows:

We derive substantially all of our income from rent received from tenants. If our tenants decide not to renew their leases, we may not be able to re-let the space. If tenants decide to renew their leases, the terms of renewals, including the cost of required improvements or concessions, may be less favorable than current lease terms. Multifamily properties are leased under operating leases with terms of generally one year or less. For the years ended 2010, 2009 2008 and 2007,2008, the multifamily tenant retention rate was 54%61%, 67%54% and 68%67%, respectively. Similar to our commercial properties, if our multifamily tenants decide not to renew their leases, we may not be able to re-let the space, or the terms of the renewal may be less favorable than current lease terms. As a result of the foregoing, our cash flow could decrease and our ability to make distributions to our shareholders could be adversely affected.

We face potential adverse effects from major tenants’tenants' bankruptcies or insolvencies.

The bankruptcy or insolvency of a major tenant may adversely affect the income produced by a property. For example, during the fourth quarter of 2008, the bankruptcy of a large retail tenant caused a loss of approximately $1.0 million. In light of the current economic recession, it is possible that additional major tenants could file for bankruptcy protection or become insolvent in the future. We cannot evict a tenant solely because of its bankruptcy. On the other hand, a court might authorize the tenant to reject and terminate its lease. In such case, our claim against the bankrupt tenant for unpaid, future rent would be subject to a statutory cap that might be substantially less than the remaining rent actually owed under the lease. As a result, our claim for unpaid rent would likely not be paid in full. This shortfall could adversely affect our cash flow and results from operations.

If a tenant experiences a downturn in its business or other types of financial distress, it may be unable to make timely rental payments. By way of illustration, provision for losses on accounts receivable from continuing operations increased to $6.7 million in 2009, from $4.2 million in 2008 and $1.9 million in 2007. This unfavorable trend could continue or worsen in 2010 and forward.

We face risks associated with property development.

Developing properties present a number of risks for us, including risks that:

Properties developed or acquired for development may generate little or no cash flow from the date of acquisition through the date of completion of development. In addition, new development activities, regardless of whether or not they are ultimately successful, may require a substantial portion of management’s time and attention.

These risks could result in substantial unanticipated delays or expenses and, under certain circumstances, could prevent completion of development activities once undertaken, any of which could have an adverse effect on our financial condition, results of operations, or ability to satisfy our debt service obligations.

We may suffer economic harm as a result of the actions of our partners in real estate joint ventures and other investments.

We may invest in joint ventures or other entities in which we are not the exclusive investor or principal decision maker. Investments in such entities may involve risks not present when a third party is not involved, including the possibility that the other parties to these investments might become bankrupt or fail to fund their share of required capital contributions. Our partners in these entities may have economic, tax or other business interests or goals which are inconsistent with our business interests or goals, and may be in a position to take actions contrary to our policies or objectives. Such investments may also lead to impasses, for example, as to whether to sell a property, because neither we nor the other parties to these investments may have full control over the entity. In addition, we may in certain circumstances be liable for the actions of the other parties to these investments. Each of these factors could have an adverse effect on our financial condition, results of operations, cash flows and ability to make distributions to our shareholders.

Our properties face significant competition.

We face significant competition from developers, owners and operators of office, medical office, retail, multifamily, industrial and other commercial real estate. Substantially all of our properties face competition from similar properties in the same market. Such competition may affect our ability to attract and retain tenants and may reduce the rents we are able to charge. These competing properties may have vacancy rates higher than our properties, which may result in their owners being willing to make space available at lower rents than the space in our properties.

We face risks associated with the use of debt, including refinancing risk.

We rely on borrowings under our credit facilities and offerings of debt securities to finance acquisitions and development activities and for general corporate purposes. The commercial real estate debt markets recentlyhave in the recent past experienced significant volatility due to a number of factors, including the tightening of underwriting standards by lenders and credit rating agencies and the reported significant inventory of unsold mortgage backed securities in the

market. The volatility resulted in investors decreasing the availability of debt financing as well as increasing the cost of debt financing. While the commercial real estate debt markets have begun to improve, weWe believe that circumstances could again arise in which we may not be able to obtain debt financing in the future on favorable terms, or at all. If we were unable to borrow under our credit facilities or to refinance existing debt financing, our financial condition and results of operations would likely be adversely affected.

We are subject to the risks normally associated with debt, including the risk that our cash flow may be insufficient to meet required payments of principal and interest. We anticipate that only a small portion of the principal of our debt will be repaid prior to maturity. Therefore, we are likely to need to refinance a significant portion of our outstanding debt as it matures. There is a risk that we may not be able to refinance existing debt or that the terms of any refinancing will not be as favorable as the terms of the existing debt. If principal payments due at maturity cannot be refinanced, extended or repaid with proceeds from other sources, such as new equity capital, our cash flow may not be sufficient to repay all maturing debt in years when significant “balloon” payments come due.

Our degree of leverage could limit our ability to obtain additional financing or affect the market price of our common shares or debt securities.

On February 25, 2010,18, 2011, our total consolidated debt was approximately $1.2 billion. Consolidated debt to consolidated market capitalization ratio, which measures total consolidated debt as a percentage of the aggregate of total consolidated debt plus the market value of outstanding equity securities, is often used by analysts to gauge leverage for equity REITs such as us. Our market value is calculated using the price per share of our common shares. Using the closing share price of $27.92$30.90 per share of our common shares on February 25, 2010,18, 2011, multiplied by the number of our common shares, our consolidated debt to total consolidated market capitalization ratio was approximately 42%38% as of February 25, 2010.18, 2011.

Our degree of leverage could affect our ability to obtain additional financing for working capital, capital expenditures, acquisitions, development or other general corporate purposes. Our senior unsecured debt is currently rated investment grade by the two major rating agencies. However, there can be no assurance that we will be able to maintain this rating, and in the event our senior debt is downgraded from its current rating, we would likely incur higher borrowing costs and/or difficulty in obtaining additional financing. Our degree of leverage could also make us more vulnerable to a downturn in business or the economy generally. There is a risk that changes in our debt to market capitalization ratio, which is in part a function of our share price, or our ratio of indebtedness to other measures of asset value used by financial analysts, may have an adverse effect on the market price of our equity or debt securities.

Rising interest rates would increase our interest costs.

We may incur indebtedness that bears interest at variable rates. Accordingly, if interest rates increase, so will our interest costs, which could adversely affect our cash flow and our ability to service debt. As a protection against rising interest rates, we may enter into agreements such as interest rate swaps, caps, floors and other interest rate exchange contracts. These agreements, however, increase our risks that other parties to the agreements may not perform or that the agreements may be unenforceable.

Covenants in our debt agreements could adversely affect our financial condition.

Our credit facilities contain customary restrictions, requirements and other limitations on our ability to incur indebtedness. We must maintain a minimum tangible net worth and certain ratios, including a maximum of total liabilities to total gross asset value, a maximum of secured indebtedness to gross asset value, a minimum of annual EBITDA to fixed charges, a minimum of unencumbered asset value to unsecured indebtedness, a minimum of net operating income from unencumbered properties to unsecured interest expense and a maximum of permitted investments to gross asset value. Our ability to borrow under our credit facilities is subject to compliance with our financial and other covenants. The recent economic downturn may adversely affect our ability to comply with these financial and other covenants.

Failure to comply with any of the covenants under our unsecured credit facilities or other debt instruments could result in a default under one or more of our debt instruments. ThisIn particular, we could suffer a default under one of our secured debt instruments that could exceed a cross default threshold under our unsecured credit facilities, causing an event of default under the unsecured credit facilities. Alternatively, even if a secured debt instrument is below the cross default threshold for non-recourse secured debt under our unsecured credit facilities, a default under such secured debt instrument may still cause a cross default under our unsecured credit facilities because such secured debt instrument may not qualify as “non-recourse” under the definition in our unsecured credit facilities. Another possible cross default could occur between our unsecured credit facilities, on the one hand, and our senior unsecured notes, on the other hand. Any of the foregoing default or cross

default events could cause our lenders to accelerate the timing of payments and/or prohibit future borrowings, either of which would have a material adverse effect on our business, operations, financial condition and liquidity.

We face risks associated with short-term liquid investments.

We have significant cash balances from time to time that we invest in a variety of short-term investments that are intended to preserve principal value and maintain a high degree of liquidity while providing current income. From time to time, these investments may include (either directly or indirectly):

Investments in these securities and funds are not insured against loss of principal. Under certain circumstances we may be required to redeem all or part of our investment, and our right to redeem some or all of our investment may be delayed or suspended. In addition, there is no guarantee that our investments in these securities or funds will be redeemable at par value. A decline in the value of our investment or a delay or suspension of our right to redeem may have a material adverse effect on our results of operations or financial condition.

Further issuances of equity securities may be dilutive to current shareholders.

The interests of our existing shareholders could be diluted if additional equity securities are issued, including to finance future developments and acquisitions, instead of incurring additional debt. Our ability to execute our business strategy depends on our access to an appropriate blend of debt financing, including unsecured lines of credit and other forms of secured and unsecured debt, and equity financing.

Compliance or failure to comply with the Americans with Disabilities Act and other laws and regulations could result in substantial costs.

The Americans with Disabilities Act generally requires that public buildings, including commercial and multifamily properties, be made accessible to disabled persons. Noncompliance could result in imposition of fines by the federal government or the award of damages to private litigants. If, pursuant to the Americans with Disabilities Act, we are required to make substantial alterations and capital expenditures in one or more of our properties, including the removal of access barriers, it could adversely affect our results of operations.

We may also incur significant costs complying with other regulations. Our properties are subject to various federal, state and local regulatory requirements, such as state and local fair housing, rent control and fire and life safety requirements. If we fail to comply with these requirements, we may incur fines or private damage awards. We believe that our properties are currently in material compliance with regulatory requirements. However, we do not know whether existing requirements will change or whether compliance with future requirements will require significant unanticipated expenditures that will adversely affect our results of operations.

Some potential losses are not covered by insurance.

We carry insurance coverage on our properties of types and in amounts that we believe are in line with coverage customarily obtained by owners of similar properties. We believe all of our properties are adequately insured. The property insurance that we maintain for our properties has historically been on an “all risk” basis, which is in full force

and effect until renewal in September 2010.August 2011. There are other types of losses, such as from wars or catastrophic events, for which we cannot obtain insurance at all or at a reasonable cost.

We have an insurance policy which has no terrorism exclusion, except for non-certified nuclear, chemical and biological acts of terrorism. Our financial condition and results of operations are subject to the risks associated with acts of terrorism and the potential for uninsured losses as the result of any such acts. Effective November 26, 2002, under this existing coverage, any losses caused by certified acts of terrorism would be partially reimbursed by the United States under a formula established by federal law. Under this formula the United States pays 85% of covered terrorism losses exceeding the statutorily established deductible paid by the insurance provider, and insurers pay 10% until aggregate insured losses from all insurers reach $100 billion in a calendar year. If the aggregate amount of insured losses under this program exceeds $100 billion during the applicable period for all insured and insurers combined, then each insurance provider will not be liable for payment of any amount which exceeds the aggregate amount of $100 billion. On December 26, 2007, the Terrorism Risk Insurance Program Reauthorization Act of 2007 was signed into law and extends the program through December 31, 2014. We continue to monitor the state of the insurance market in general, and the scope and costs of coverage for acts of terrorism in particular, but we cannot anticipate what amount of coverage will be available on commercially reasonable terms in future policy years.

In the event of an uninsured loss or a loss in excess of our insurance limits, we could lose both the revenues generated from the affected property and the capital we have invested in the affected property. Depending on the specific circumstances of the affected property it is possible that we could be liable for any mortgage indebtedness or other obligations related to the property. Any such loss could adversely affect our business and financial condition and results of operations.

We have to renew our policies in most cases on an annual basis and negotiate acceptable terms for coverage, exposing us to the volatility of the insurance markets, including the possibility of rate increases. Any material increase in insurance rates or decrease in available coverage in the future could adversely affect our results of operations and financial condition.

Actual or threatened terrorist attacks may adversely affect our ability to generate revenues and the value of our properties.

All of our properties are located in or near Washington D.C., a metropolitan area that has been and may in the future be the target of actual or threatened terrorism attacks. As a result, some tenants in our market may choose to relocate their businesses to other markets. This could result in an overall decrease in the demand for commercial space in this market generally, which could increase vacancies in our properties or necessitate that we lease our properties on less favorable terms, or both. In addition, future terrorist attacks in or near Washington D.C. could directly or indirectly damage our properties, both physically and financially, or cause losses that materially exceed our insurance coverage. As a result of the foregoing, our ability to generate revenues and the value of our properties could decline materially.

Potential liability for environmental contamination could result in substantial costs.

Under federal, state and local environmental laws, ordinances and regulations, we may be required to investigate and clean up the effects of releases of hazardous or toxic substances or petroleum products at our properties, regardless of our knowledge or responsibility, simply because of our current or past ownership or operation of the real estate. In addition, the U.S. Environmental Protection Agency, the U.S. Occupational Safety and Health Administration and other state and local governmental authorities are increasingly involved in indoor air quality standards, especially with respect to asbestos, mold, medical waste and lead-based paint. The clean up of any environmental contamination, including asbestos and mold, can be costly. If environmental problems arise, we may have to make substantial payments which could adversely affect our financial condition and results of operations because:

These costs could be substantial and in extreme cases could exceed the value of the contaminated property. The presence of hazardous or toxic substances or petroleum products or the failure to properly remediate contamination may adversely affect our ability to borrow against, sell or rent an affected property. In addition, applicable environmental laws create liens on contaminated sites in favor of the government for damages and costs it incurs in connection with a contamination.

Environmental laws also govern the presence, maintenance and removal of asbestos. Such laws require that owners or operators of buildings containing asbestos:

Such laws may impose fines and penalties on building owners or operators who fail to comply with these requirements and may allow third parties to seek recovery from owners or operators for personal injury associated with exposure to asbestos fibers.

It is our policy to retain independent environmental consultants to conduct Phase I environmental site assessments and asbestos surveys with respect to our acquisition of properties. These assessments generally include a visual inspection of the properties and the surrounding areas, an examination of current and historical uses of the properties and the surrounding areas and a review of relevant state, federal and historical documents. However, they do not always involve invasive techniques such as soil and ground water sampling. Where appropriate, on a property-by-property basis, our general practice is to have these consultants conduct additional testing. However, even though these additional assessments may be conducted, there is still the risk that:

Failure to qualify as a REIT would cause us to be taxed as a corporation, which would substantially reduce funds available for payment of dividends.

If we fail to qualify as a REIT for federal income tax purposes, we would be taxed as a corporation. We believe that we are organized and qualified as a REIT and intend to operate in a manner that will allow us to continue to qualify as a REIT. However, we cannot assure you that we are qualified as such, or that we will remain qualified as such in the future. This is because qualification as a REIT involves the application of highly technical and complex provisions of the

Internal Revenue Code as to which there are only limited judicial and administrative interpretations and involves the determination of facts and circumstances not entirely within our control. Future legislation, new regulations, administrative interpretations or court decisions may significantly change the tax laws or the application of the tax laws with respect to qualification as a REIT for federal income tax purposes or the federal income tax consequences of such qualification.

If we fail to qualify as a REIT we could face serious tax consequences that could substantially reduce our funds available for payment of dividends for each of the years involved because:

In addition, if we fail to qualify as a REIT, we would no longer be required to pay dividends. As a result of these factors, our failure to qualify as a REIT could have a material adverse impact on our results of operations, financial condition and liquidity.

The market value of our securities can be adversely affected by many factors.

As with any public company, a number of factors may adversely influence the public market price of our common shares. These factors include:

We cannot assure you we will continue to pay dividends at historical rates.

Our ability to continue to pay dividends on our common shares at historical rates or to increase our common share dividend rate will depend on a number of factors, including, among others, the following:

If we do not maintain or increase the dividend rate on our common shares in the future, it could have an adverse effect on the market price of our common shares.

Provisions of the Maryland General Corporation Law, or the MGCL, may limit a change in control.

There are several provisions of the Maryland General Corporation Law, or the MGCL, that may limit the ability of a third party to undertake a change in control, including:

These provisions may delay, defer, or prevent a transaction or a change in control that may involve a premium price for holders of our shares or otherwise be in their best interests.

ITEM 1B: UNRESOLVED STAFF COMMENTS

None.

ITEM 2:

PROPERTIES

ITEM 2: PROPERTIES

The schedule on the following pages lists our real estate investment portfolio as of December 31, 2009,2010, which consisted of 9085 properties and land held for development.

As of December 31, 2009,2010, the percent leased is the percentage of net rentable area for which fully executed leases exist and may include signed leases for space not yet occupied by the tenant.

Cost information is included in Schedule III to our financial statements included in this Annual Report on Form 10-K.

Schedule of Properties

SCHEDULE OF PROPERTIES (continued)

SCHEDULE OF PROPERTIES (continued)

ITEM 3: LEGAL PROCEEDINGS

None.

No matters were submitted to a vote of security holders during the fourth quarter of 2009.

PART II

ITEM 5: MARKET FOR THE REGISTRANT’S COMMON EQUITY, RELATED STOCKHOLDER MATTERS AND ISSUER PURCHASES OF EQUITY SECURITIES

Our shares trade on the New York Stock Exchange. Currently, there are approximately 6,4846,130 shareholders of record.

The high and low sales price for our shares for 20092010 and 2008,2009, by quarter, and the amount of dividends we paid per share are as follows:

We have historically paid dividends on a quarterly basis. Dividends are primarily paid from our cash flow from operating activities.

During the period covered by this report, we did not sell equity securities without registration under the Securities Act.

Neither we nor any affiliated purchaser (as that term is defined in Securities Exchange Act Rule 10b-18(a) (3)) made any repurchases of our shares during the fourth quarter of the fiscal year covered by this report.

ITEM 6:

SELECTED FINANCIAL DATA

ITEM 6: SELECTED FINANCIAL DATA

The following table sets forth our selected financial data on a historical basis, which has been revised for properties disposed of or classified as held for sale (see note 3 to the consolidated financial statements). The following data should be read in conjunction with our financial statements and notes thereto and Management’s Discussion and Analysis of Financial Condition and Results of Operations included elsewhere in this Form 10-K.

ITEM 7:

MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

ITEM 7: MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

Our Management’s Discussion and Analysis of Financial Conditions and Results of Operations (“MD&A”) is provided in addition to the accompanying consolidated financial statements and notes to assist readers in understanding our results of operations and financial condition. MD&A is organized as follows:

When evaluating our financial condition and operating performance, we focus on the following financial and non-financial indicators:

Overview

Business

Our revenues are derived primarily from the ownership and operation of income-producing properties in the greater Washington metro region. As of December 31, 2009,2010, we owned a diversified portfolio of 9085 properties, totaling approximately 10.910.7 million square feet of commercial space and 2,540 multifamily units.units, and land held for development. These 9085 properties consisted of 2725 office properties, 2016 industrial/flex properties, 18 medical office properties, 1415 retail centers and 11 multifamily properties and land held for development.properties.