1
 
                                                                     EXHIBIT 5.1
 
                        [SULLIVAN & CROMWELL LETTERHEAD]
 
                                                                January 12, 1998
 
H. F. Ahmanson & Company
4900 Rivergrade Road,
Irwindale, CA 91706
 
Dear Sirs:
 
     In connection with the registration under the Securities Act of 1933 (the
"Act") of 16,393,012 shares (the "Securities") of Common Stock, par value $.01
per share, of H. F. Ahmanson & Company, a Delaware corporation (the "Company"),
we, as your counsel, have examined such corporate records, certificates and
other documents, and such questions of law, as we have considered necessary or
appropriate for the purposes of this opinion. Upon the basis of such
examination, we advise you that, in our opinion, when the registration statement
relating to 15,993,092 of the Securities (the "Registration Statement") has
become effective under the Act and a registration statement pursuant to Rule
462(b) under the Act relating to 399,920 of the Securities has been filed and
has become effective under the Act, the Securities have been duly issued and
sold as contemplated by the Registration Statement and the merger of Coast
Savings Financial, Inc. with and into the Company has been consummated, the
Securities will be validly issued, fully paid and nonassessable.
 
     The foregoing opinion is limited to the Federal laws of the United States
and the General Corporation Law of the State of Delaware, and we are expressing
no opinion as to the effect of the laws of any other jurisdiction.
 
     Also, we have relied as to certain matters on information obtained from
public officials, officers of the Company and other sources believed by us to be
responsible.
 
     We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to us under the heading "Validity of
Ahmanson Common Stock" in the Prospectus and to the incorporation by reference
of this opinion (and consent) in a registration statement to be filed by
Ahmanson pursuant to Rule 462(b) under the Act. In giving such consent, we do
not thereby admit that we are in the category of persons whose consent is
required under Section 7 of the Act.
 
                                          Very truly yours,
 
                                          /s/ SULLIVAN & CROMWELL