Exhibit 5.1

                    [LETTERHEAD OF SULLIVAN & WORCESTER LLP]

                                                              December 5, 2001

Five Star Quality Care, Inc.
400 Centre Street
Newton, Massachusetts 02458

         Re: REGISTRATION STATEMENT ON FORM S-1 (FILE NO. 333-69846)
             REGARDING THE REGISTRATION OF 4,352,170 SHARES OF COMMON
             STOCK, PAR VALUE $.01 PER SHARE
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Ladies and Gentlemen:

         In connection with the registration under the Securities Act of 1933,
as amended (the "Act"), by Five Star Quality Care, Inc., a Maryland corporation
(the "Company"), of 4,352,170 shares of its common stock, par value $.01 per
share (the "Common Shares"), the following opinion is furnished to the Company
to be filed with the Securities and Exchange Commission (the "Commission") as
Exhibit 5.1 to the Company's registration statement on Form S-1, Registration
No. 333-69846 (the "Registration Statement"). The Registration Statement
describes the distribution of the Common Shares by Senior Housing Properties
Trust, a Maryland real estate investment trust ("Senior Housing"), to the
holders of Senior Housing common shares of beneficial interest, including HRPT
Properties Trust, who will in turn distribute the Common Shares to holders of
HRPT Properties Trust common shares of beneficial interest (the "Distribution").

         We have acted as counsel to the Company in connection with the
Distribution, and we have examined originals or copies, certified or otherwise
identified to our satisfaction, of the Registration Statement, the form of
transaction agreement to be entered into by the Company, Senior Housing and
other parties in connection with the Distribution, the Company's articles of
amendment and restatement and the amended and restated bylaws currently in
effect, and such corporate records, certificates and statements of officers of
the Company, of the Company's accountants and of public officials, and such
other documents as we have considered necessary in order to furnish the opinion
hereinafter set forth.

         We express no opinion herein as to the laws of any jurisdiction other
than the Commonwealth of Massachusetts and the federal law of the United States,
and we express no opinion as to state securities or blue sky laws. Insofar as
this opinion involves matters of Maryland law, we have, with your permission,
relied solely upon the opinion of Ballard Spahr Andrews & Ingersoll, LLP, a copy
of which is being filed herewith as Exhibit 5.2 to the



Five Star Quality Care, Inc.
December 5, 2001
Page 2

Registration Statement, and our opinion is subject to the exceptions,
assumptions, qualifications and limitations therein expressed.

         Based upon and subject to the foregoing, we are of the opinion that,
when issued in the Distribution, the Common Shares distributed will be duly
authorized, validly issued, fully paid and nonassessable by the Company.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the references to our firm in the prospectus
forming a part of the Registration Statement. 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 the rules and regulations of the
Commission promulgated thereunder.

                                           Very truly yours,

                                           /s/ Sullivan & Worcester LLP

                                           SULLIVAN & WORCESTER LLP