Exhibit 8.1 SULLIVAN & WORCESTER LLP ONE POST OFFICE SQUARE BOSTON, MASSACHUSETTS 02109 (617) 338-2800 FAX NO. 617-338-2880 IN WASHINGTON, D.C. IN NEW YORK CITY 1025 CONNECTICUT AVENUE, N.W. 767 THIRD AVENUE WASHINGTON, D.C. 20036 NEW YORK, NEW YORK 10017 (202) 775-8190 (212) 486-8200 FAX NO. 202-293-2275 FAX NO. 212-758-2151 March 30, 2000 Senior Housing Properties Trust 400 Centre Street Newton, Massachusetts 02458 Ladies and Gentlemen: In connection with the filing by Senior Housing Properties Trust, a Maryland real estate investment trust (the "Company"), of its Annual Report on Form 10-K for the year ended December 31, 1999 (the "Form 10-K"), under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), the following opinion is furnished to you to be filed with the Securities and Exchange Commission (the "SEC") as Exhibit 8.1 to the Form 10-K. We have acted as counsel for the Company in connection with the preparation of its Form 10-K, and we have examined originals or copies, certified or otherwise identified to our satisfaction, of corporate records, certificates and statements of officers and accountants of the Company and of public officials, and such other documents as we have considered relevant and necessary in order to furnish the opinion hereinafter set forth. Specifically, and without limiting the generality of the foregoing, we have reviewed: (i) the declaration of trust, as amended and restated, and the by-laws of the Company, as amended and restated; and (ii) the sections in the Company's Form 10-K captioned "Federal Income Tax Considerations" and "ERISA Plans, Keogh Plans and Individual Retirement Accounts." With respect to all questions of fact on which such opinions are based, we have assumed the accuracy and completeness of and have relied on the information set forth in the Form 10-K and in the documents incorporated therein by reference, and on representations made to us by officers of the Company. We have not independently verified such information. The opinion set forth below is based upon the Internal Revenue Code of 1986, as amended, the Treasury Regulations issued thereunder, published administrative interpretations thereof, and judicial decisions with respect thereto, all as of the date hereof (collectively, the "Tax Laws"), and upon the Employee Retirement Income Security Act of 1974, as amended, the Department of Labor regulations issued thereunder, published administrative interpretations thereof, and judicial decisions with respect thereto, all as of the date hereof (collectively, the Senior Housing Properties Trust March 30, 2000 Page 2 "ERISA Laws"). No assurance can be given that the Tax Laws or the ERISA Laws will not change. In preparing the discussions with respect to Tax Laws and ERISA Laws matters in the sections of the Annual Report captioned "Federal Income Tax Considerations" and "ERISA Plans, Keogh Plans and Individual Retirement Accounts," we have made certain assumptions and expressed certain conditions and qualifications therein, all of which assumptions, conditions and qualifications are incorporated herein by reference. Based upon and subject to the foregoing, we are of the opinion that the discussions with respect to Tax Laws and ERISA Laws matters in the sections of the Annual Report captioned "Federal Income Tax Considerations" and "ERISA Plans, Keogh Plans and Individual Retirement Accounts," in all material respects are accurate and fairly summarize the Tax Laws issues and ERISA Laws issues addressed therein, and hereby confirm that the opinions of counsel referred to in said sections represent our opinions on the subject matter thereof. We hereby consent to the incorporation of this opinion by reference as an exhibit to the Form 10-K and to the reference of our firm therein. In giving such consent, we do not thereby admit that we come within the category of persons whose consent is required under Section 7 of the Act or under the rules and regulations of the SEC promulgated thereunder. Very truly yours, /s/ SULLIVAN & WORCESTER LLP SULLIVAN & WORCESTER LLP