1
 
                                                                     EXHIBIT 5.1
   
                               November 18, 1997
    
 
Cellegy Pharmaceuticals, Inc.
1065 E. Hillsdale Blvd.
Suite 418
Foster City, CA 94404
 
Gentlemen/Ladies:
 
   
     At your request, we have examined the Registration Statement on Form S-1
(the "Registration Statement") filed by you with the Securities and Exchange
Commission (the "Commission") on or about October 17, 1997, as amended, in
connection with the registration under the Securities Act of 1933, as amended,
of an aggregate of 2,012,500 shares of your Common Stock (the "Stock"), all of
which will be sold by the Company.
    
 
     In rendering this opinion, we have examined the following:
 
          (1) the Registration Statement, together with the Exhibits filed as a
     part thereof;
 
          (2) your registration statement on Form 8-A filed with the Commission
     in connection with the Company's initial public offering in August 1995;
 
          (3) the Prospectus prepared in connection with the Registration
     Statement;
 
          (4) the minutes of meetings and actions by written consent of the
     Board of Directors that are contained in your minute books and that are in
     our possession, that relate to issuance of the Stock;
 
          (5) the articles of incorporation of the Company as amended through
     the date of this opinion and the Bylaws of the Company, both certified by
     the Secretary of the Company on October 17, 1997; and
 
          (6) a Management Certificate addressed to us and dated of even date
     herewith executed by the Company containing certain factual and other
     representations.
 
     In our examination of documents for purposes of this opinion, we have
assumed, and express no opinion as to, the genuineness of all signatures on
original documents, the authenticity of all documents submitted to us as
originals, the conformity to originals of all documents submitted to us as
copies, the legal capacity of all natural persons executing the same, the lack
of any undisclosed terminations, modifications, waivers or amendments to any
documents reviewed by us and the due execution and delivery of all documents
where due execution and delivery are prerequisites to the effectiveness thereof.
 
     As to matters of fact relevant to this opinion, we have relied solely upon
our examination of the documents referred to above and have assumed the current
accuracy and completeness of the information obtained from records included in
the documents referred to above. We have made no independent investigation or
other attempt to verify the accuracy of any of such information or to determine
the existence or non-existence of any other factual matters; however, we are not
aware of any facts that would lead us to believe that the opinion expressed
herein is not accurate.
 
     In rendering any opinion that the shares of Stock are, or will when issued
be, "fully paid," we have assumed that such shares will be issued in accordance
with the terms of the underwriting agreement attached as an exhibit to the
Registration Statement, and that the Company will receive full consideration for
the issuance of such shares provided for in such agreement.
 
     Based upon the foregoing, it is our opinion that the shares of Stock to be
sold by the Company pursuant to the Registration Statement are legally issued
and nonassessable and, to our knowledge, fully paid.
 
     We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to all references to us, if any, in the
Registration Statement, the Prospectus constituting a part thereof and any
amendments thereto.
 
     This opinion speaks only as of its date and is intended solely for your use
as an exhibit to the Registration Statement for the purpose of the above sale of
the Stock and is not to be relied upon for any other purpose.
 
                                       Very truly yours,
 
                                       FENWICK & WEST LLP
                                       By: /s/ Fenwick & West LLP