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                                                                     Exhibit 5.1

                           SIDLEY AUSTIN BROWN & WOOD
                A PARTNERSHIP INCLUDING PROFESSIONAL CORPORATIONS


     DALLAS                       BANK ONE PLAZA                   BEIJING
                               10 S. DEARBORN STREET
  LOS ANGELES                 CHICAGO, ILLINOIS 60603             HONG KONG
                              TELEPHONE 312 853 7000
    NEW YORK                  FACSIMILE 312 853 7036                LONDON
                                  www.sidley.com
 SAN FRANCISCO                                                     SHANGHAI
                                   FOUNDED 1866
    SEATTLE                                                       SINGAPORE

WASHINGTON, D.C.                                                     TOKYO






                                 August 24, 2001



Starwood Hotels & Resorts Worldwide, Inc.
Starwood Hotels & Resorts
1111 Westchester Avenue
White Plains, New York 10604


                  Re:      Registration Statement on Form S-3 of Starwood Hotels
                           & Resorts Worldwide, Inc. and Starwood Hotels &
                           Resorts

Ladies and Gentlemen:


                  We are counsel to Starwood Hotels & Resorts Worldwide, Inc., a
Maryland corporation (the "Corporation"), and Starwood Hotels & Resorts, a
Maryland real estate investment trust (the "Trust" and, together with the
Corporation, the "Company"), and have represented the Company with respect to
the Registration Statement on Form S-3, as amended (as so amended, the
"Registration Statement"), filed by the Company with the Securities and Exchange
Commission (the "Commission") under the Securities Act of 1933, as amended (the
"Securities Act"), relating to the registration of securities (the "Securities")
of the Corporation and the Trust with an aggregate offering price of
$3,000,000,000 (or equivalent amounts in one or more other currencies based on
the applicable exchange rate at the respective times of sale), consisting of (i)
shares of common stock, $.01 par value per share, of the Corporation (the
"Corporation Shares") and Class B shares of beneficial interest, $.01 par value
per share, of the Trust (the "Trust Shares"), which are attached and traded as
units consisting of one Corporation Share and one Trust Share (the "Shares");
(ii) shares of preferred stock, $.01 par value per share, of the Corporation
(the "Corporation Preferred Shares") and preferred shares of beneficial
interest, $.01 par value per share, of the Trust (the "Trust Preferred Shares"
and, together with the Corporation Preferred Shares, the "Preferred Shares"),
which may, but are not required to, be attached and traded as units with
preferred stock or shares of the other entity, and which may be represented by
depositary shares ("Depositary Shares"); (iii) secured or unsecured debt
securities of the Corporation and/or the Trust consisting of notes, debentures
and other evidences of indebtedness (the "Debt Securities"); (iv) (A) warrants
to purchase Corporation Shares and warrants to purchase Trust Shares that are
attached and traded as units consisting of one warrant to purchase Corporation
Shares and one warrant to purchase a like number of Trust Shares, (B) warrants
to purchase Corporation Preferred Shares and/or Trust Preferred Shares, and (C)
warrants to purchase Debt Securities (collectively, the "Warrants"); and (v)
convertible notes of


          SIDLEY AUSTIN BROWN & WOOD IS AN ILLINOIS GENERAL PARTNERSHIP
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SIDLEY AUSTIN BROWN & WOOD                                               CHICAGO


Starwood Hotels & Resorts Worldwide, Inc.
Starwood Hotels & Resorts
August 24, 2001
Page 2




the Corporation and the Trust that may be issued to underwriters to facilitate
an underwritten public offering of equity securities of the Corporation and the
Trust (the "Convertible Notes").


                  Unless otherwise specified in the applicable Prospectus
Supplement, the Debt Securities will be issued under an indenture between the
Corporation and/or the Trust and a trustee to be named (the "Debt Trustee"),
substantially in the form of one of the indentures filed as an exhibit to the
Registration Statement (any such indenture, as amended or supplemented from time
to time, the "Debt Indenture").


                  Whenever the Company elects to have Preferred Shares be
represented by Depositary Shares, such Preferred Shares underlying the
Depositary Shares will be deposited under a deposit agreement (each, a "Deposit
Agreement") with a bank or trust company identified therein, as preferred stock
depositary (the "Preferred Stock Depositary"), substantially in the form filed
prior to the issuance of any Depositary Shares in an amendment to the
Registration Statement or incorporated by reference therein pursuant to a
Current Report on Form 8-K of the Company.

                  Each series of Warrants will be issued under a Warrant
Agreement (each, a "Warrant Agreement") with a bank or trust company identified
therein, as warrant agent (the "Warrant Agent"), substantially in the form filed
prior to the issuance of any Warrants in an amendment to the Registration
Statement or incorporated by reference therein pursuant to a Current Report on
Form 8-K of the Company.

                  Each series of Convertible Notes will be issued under an
indenture among the Corporation, the Trust and a trustee to be named (the
"Convertible Note Trustee"), substantially in the form filed prior to the
issuance of any Convertible Notes in an amendment to the Registration Statement
or incorporated by reference as an exhibit to the Registration Statement (such
indenture, as amended or supplemented from time to time, the "Convertible Note
Indenture").

                  In rendering the opinions expressed below, we have examined
and relied upon a copy of the Registration Statement. We have also examined
originals, or copies of originals certified to our satisfaction, of such
agreements, documents, certificates and other statements of governmental
officials and other instruments, and have examined such questions of law and
have satisfied ourselves as to such matters of fact, as we have considered
relevant and necessary as a basis for this opinion. We have assumed the
authenticity of all documents submitted to us as originals, the genuineness of
all signatures, the legal capacity of all natural persons and the conformity
with the original documents of any copies thereof submitted to us for our
examination.
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SIDLEY AUSTIN BROWN & WOOD                                               CHICAGO


Starwood Hotels & Resorts Worldwide, Inc.
Starwood Hotels & Resorts
August 24, 2001
Page 3




                  Based on the foregoing and subject to the qualifications and
limitations set forth below, it is our opinion that:

                  1.       Each series of Debt Securities will be legally issued
and valid and binding obligations of the Corporation or the Trust, as the case
may be (except to the extent enforceability may be limited by applicable
bankruptcy, insolvency, reorganization, moratorium, fraudulent transfer or other
similar laws affecting the enforcement of creditors' rights generally and by the
effect of general principles of equity, regardless of whether enforceability is
considered in a proceeding in equity or at law), when (i) the Registration
Statement, as finally amended (including any necessary post-effective
amendments), shall have become effective under the Securities Act and the Debt
Indenture shall have been qualified under the Trust Indenture Act of 1939, as
amended, and the Debt Indenture shall have been duly authorized, executed and
delivered by the Corporation or the Trust, as applicable, and duly executed and
delivered by the Debt Trustee; (ii) a Prospectus Supplement with respect to such
series of Debt Securities shall have been filed with the Commission in
compliance with the Securities Act and the rules and regulations thereunder;
(iii) the Corporation's Board of Directors or a duly authorized committee
thereof, or the Trust's Board of Trustees or a duly authorized committee
thereof, as the case may be, shall have duly adopted final resolutions
authorizing the issuance and sale of such series of Debt Securities as
contemplated by the Registration Statement and the Debt Indenture; and (iv) such
series of Debt Securities shall have been duly executed by the Corporation or
the Trust, as the case may be, authenticated by the Debt Trustee as provided in
the Debt Indenture and the final authorizing resolutions and duly delivered to
the purchasers thereof against payment of the agreed consideration therefor, as
provided in the Registration Statement and any Prospectus Supplement relating
thereto.

                  2.       Each issue of Depositary Shares will be validly
issued and will entitle the holders of depositary receipts evidencing such
Depositary Shares to the rights specified in the Deposit Agreement relating to
such Depositary Shares (except to the extent enforceability may be limited by
applicable bankruptcy, insolvency, reorganization, moratorium, fraudulent
transfer or other similar laws affecting the enforcement of creditors' rights
generally and by the effect of general principles of equity, regardless of
whether enforceability is considered in a proceeding in equity or at law), when
(i) the Registration Statement, as finally amended (including any necessary
post-effective amendments), shall have become effective under the Securities
Act; (ii) a Prospectus Supplement with respect to the Depositary Shares and the
series of Preferred Shares underlying such Depositary Shares shall have been
filed with the Commission in compliance with the Securities Act and the rules
and regulations thereunder; (iii) the Deposit Agreement relating to such
Depositary Shares shall have been duly authorized, executed and delivered by the
Corporation or the Trust, as applicable, and duly executed and delivered by the
Preferred Stock Depositary; (iv) the Corporation's Board of Directors or a duly
authorized committee thereof or the Trust's Board of Trustees or a duly
authorized committee thereof, as the case may be, shall have duly adopted final
resolutions in conformity with the charter of the Corporation or
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SIDLEY AUSTIN BROWN & WOOD                                               CHICAGO


Starwood Hotels & Resorts Worldwide, Inc.
Starwood Hotels & Resorts
August 24, 2001
Page 4




the Declaration of Trust of the Trust, as the case may be, establishing the
terms and conditions of the series of Preferred Shares underlying the Depositary
Shares and authorizing the sale of such series of Preferred Shares as
contemplated by the Registration Statement and any Prospectus Supplement
relating thereto; (v) appropriate articles supplementary with respect to the
series of Preferred Shares underlying the Depositary Shares shall have been
filed with, and accepted for record by, the State Department of Assessments and
Taxation of Maryland; (vi) certificates representing such series of Preferred
Shares shall have been duly executed, countersigned and registered and duly
delivered to the purchasers thereof against payment of the agreed consideration
therefor (which consideration shall be not less than $.01 per share); and (vii)
the depositary receipts evidencing Depositary Shares shall have been duly
executed and delivered by the Preferred Stock Depositary in the manner set forth
in the Deposit Agreement.

                  3.       Each issue of Warrants will be legally issued and
valid and binding obligations of the Corporation or the Trust, as the case may
be (except to the extent enforceability may be limited by applicable bankruptcy,
insolvency, reorganization, moratorium, fraudulent transfer or other similar
laws affecting the enforcement of creditors' rights generally and by the effect
of general principles of equity, regardless of whether enforceability is
considered in a proceeding in equity or at law), when (i) the Registration
Statement, as finally amended (including any necessary post-effective
amendments), shall have become effective under the Securities Act; (ii) a
Prospectus Supplement with respect to such issue of Warrants shall have been
filed with the Commission in compliance with the Securities Act and the rules
and regulations thereunder; (iii) the Warrant Agreement relating to such issue
of Warrants shall have been duly authorized, executed and delivered by the
Corporation or the Trust, as applicable, and duly executed and delivered by the
Warrant Agent; (iv) the Corporation's Board of Directors or a duly authorized
committee thereof or the Trust's Board of Trustees or a duly authorized
committee thereof, as the case may be, shall have duly adopted final resolutions
in conformity with the charter of the Corporation or the Declaration of Trust of
the Trust, as the case may be, setting forth the terms of such issue of Warrants
and authorizing the issuance and sale of the Warrants as contemplated by the
Registration Statement and any Prospectus Supplement relating thereto; and (v)
the Warrants shall have been duly executed, authenticated by the Warrant
Agent(s) and registered and duly delivered to the purchasers thereof against
payment of the agreed consideration therefor, as provided in the Registration
Statement and any Prospectus Supplement relating thereto and the final
authorizing resolutions and the Warrant Agreement(s) applicable thereto.

                  4.       Each series of Convertible Notes will be legally
issued and valid and binding obligations of the Corporation and the Trust
(except to the extent enforceability may be limited by applicable bankruptcy,
insolvency, reorganization, moratorium, fraudulent transfer or other similar
laws affecting the enforcement of creditors' rights generally and by the effect
of general principles of equity, regardless of whether enforceability is
considered in a proceeding in equity or at law) when (i) the Registration
Statement, as finally amended (including any
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SIDLEY AUSTIN BROWN & WOOD                                               CHICAGO


Starwood Hotels & Resorts Worldwide, Inc.
Starwood Hotels & Resorts
August 24, 2001
Page 5




necessary post-effective amendments), shall have become effective under the
Securities Act and the Convertible Note Indenture shall have been qualified
under the Trust Indenture Act of 1939, as amended, and the Convertible Note
Indenture shall have been duly authorized, executed and delivered by the
Corporation and the Trust and duly executed and delivered by the Convertible
Note Trustee; (ii) a Prospectus Supplement with respect to such Convertible
Notes and the Shares issuable upon conversion of the Convertible Notes shall
have been filed with the Commission in compliance with the Securities Act and
the rules and regulations thereunder; (iii) each of the Corporation's Board of
Directors or a duly authorized committee thereof and the Trust's Board of
Trustees or a duly authorized committee thereof shall have duly adopted final
resolutions in conformity with the charter of the Corporation or the Declaration
of Trust of the Trust, as the case may be, authorizing the issuance and sale of
the Convertible Notes as contemplated by the Registration Statement and any
Prospectus Supplement relating thereto; and (iv) such series of Convertible
Notes shall have been duly executed by the Corporation and the Trust and
authenticated by the Convertible Note Trustee as provided in the Convertible
Note Indenture and the final authorizing resolutions and shall have been duly
delivered to the purchasers thereof against payment of the agreed consideration
therefor as provided in the Registration Statement and any Prospectus Supplement
relating thereto.

                  For the purposes of this opinion letter, we have assumed that,
at the time of the issuance, sale and delivery of each series of Debt
Securities, each issue of Warrants, each issue of Depositary Shares or each
series of Convertible Notes, as the case may be: (i) the authorization thereof
by the Corporation or the Trust, as applicable, will not have been modified or
rescinded, and there will not have occurred any change in law affecting the
validity, legally binding character or enforceability thereof; (ii) in the case
of the issue of Debt Securities, the form of Debt Indenture will not have been
modified or amended; (iii) in the case of the issue of Warrants, the terms and
conditions of such Warrants and the related Warrant Agreement will be as
expressly contemplated by the Registration Statement; (iv) in the case of the
issue of Depositary Shares, the terms and conditions of the Depositary Shares
and underlying series of Preferred Shares and the related Depositary Agreement
will be as expressly contemplated by the Registration Statement; and (v) the
charter of the Corporation, as currently in effect, and the Declaration of Trust
of the Trust, as currently in effect, will not have been modified or amended and
will be in full force and effect.

                  We do not find it necessary for the purposes of this opinion
letter to cover, and accordingly we express no opinion as to, the application of
the securities or blue sky laws of the various states to the sale of the
Securities. Except as expressly stated in the second following sentence, this
opinion letter is limited to the laws of the State of New York and the
Securities Act. For the purposes of this opinion letter, we have assumed that
the Debt Indenture, each Warrant Agreement, each Deposit Agreement and the
Convertible Note Indenture will be governed by the laws of the State of New
York. Insofar as the opinions expressed above relate to matters governed by the
laws of the State of Maryland, we have not made an independent
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SIDLEY AUSTIN BROWN & WOOD                                               CHICAGO


Starwood Hotels & Resorts Worldwide, Inc.
Starwood Hotels & Resorts
August 24, 2001
Page 6




examination of such laws, but have relied exclusively as to such laws, subject
to the exceptions, qualifications and limitations therein expressed, upon the
opinion letter of Ballard Spahr Andrews & Ingersoll, LLP of Baltimore, Maryland,
a copy of which has been separately provided to you and is being separately
filed as an Exhibit to the Registration Statement.

                  We hereby consent to the filing of this opinion letter as an
Exhibit to the Registration Statement and to all references to our firm included
in or made a part of the Registration Statement.


                                           Very truly yours,



                                           /s/ Sidley Austin Brown & Wood