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                                                                     EXHIBIT 5.1
 
                           [LETTERHEAD OF BRYAN CAVE]
 
                                                                January   , 1998
 
Medicis Pharmaceutical Corporation
4343 East Camelback Road, Suite 250
Phoenix, Arizona 85018-2700
 
Re:  Medicis Pharmaceutical Corporation
     Registration Statement on Form S-3
 
Ladies and Gentlemen:
 
     We have acted as counsel to Medicis Pharmaceutical Corporation, a Delaware
corporation (the "Company") in connection with the registration under the
Securities Act of 1933, as amended (the "Securities Act"), of the proposed
public offering by the Company of 3,000,000 shares of the Common Stock of the
Company (the "Common Stock") (3,450,000 shares if the over-allotment option
granted by the Company to the Underwriters is exercised in full). The Common
Stock is to be registered pursuant to a registration statement on Form S-3 (the
"Registration Statement") filed with the Securities and Exchange Commission (the
"Commission"). Capitalized terms used herein without definition shall have the
meaning set forth in the Registration Statement.
 
     In arriving at the opinion expressed below, we have examined the
Registration Statement and such other documents, including the Certificate of
Incorporation and Bylaws of the Company, each as amended to date, as we have
deemed necessary to enable us to express the opinion set forth herein. In
addition, we have examined and relied, to the extent we deem proper, on
certificates of officers of the Company as to certain factual matters relevant
to this opinion and other written and oral representations made to us by the
officers of the Company, and on the originals or copies, certified or otherwise
identified to our satisfaction as conforming to the originals thereof, of such
other documents and corporate records of the Company and such other instruments
and certificates of public officials and other persons as we have deemed
appropriate. In our examination, we have assumed the authenticity of all
documents submitted to us as originals, the conformity to the original documents
of all documents submitted to us as copies, and the genuineness of all
signatures (other than that of the Company) on all documents reviewed by us.
 
     Based on the foregoing and subject to the limitations and qualifications
set forth herein, we are of the opinion that:
 
     The Common Stock to be issued by the Company, pursuant to the terms of the
Registration Statement and an Underwriting Agreement to be entered into by the
Company and BancAmerica Robertson Stephens, as Representative of the several
Underwriters, have been duly authorized, and upon issuance and delivery against
payment therefor in accordance with the terms of such Underwriting Agreement,
will be duly and validly issued and fully paid and nonassessable.
 
     This opinion is limited to the present laws of the State of Delaware and
the present federal Securities laws of the United States and to the facts as
they presently exist. We hereby consent to references to our firm under the
caption "Legal Matters" in the Registration Statement and to the use of this
opinion as an exhibit to the Registration Statement. In giving this consent, we
do not hereby admit that we come within the category of persons whose consent is
required under Section 7 of the Securities Act, or the rules and regulations of
the Commission thereunder.
 
                                          Very truly yours,
 
                                          /s/ BRYAN CAVE LLP
 
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                                          Bryan Cave LLP