EXHIBIT 5.1

                   [LETTERHEAD OF FNB FINANCIAL SERVICES, LP]

                                January 24, 2005

FNB Financial Services, LP
103 Foulk Road, Suite 202
Wilmington, Delaware  19803

F.N.B. Corporation
One F.N.B. Boulevard
Hermitage, Pennsylvania  16148

Ladies and Gentlemen:

      I have acted as counsel to FNB Financial Services, LP (the "Company") and
F.N.B. Corporation, a Florida corporation ("FNB"), in connection with the
preparation and filing with the Securities and Exchange Commission of a
Registration Statement on Form S-4 (the "Registration Statement") relating to
the registration under the Securities Act of 1933, as amended, of the issuance
and sale by the Company of up to $350,000,000 aggregate principal amount of (i)
Nonnegotiable Subordinated Term Notes, Series 2005, due 3, 6, 9, 12, 15, 18, 21,
24, 27, 30, 36, 48, 60, 84 and 120 Months (in the aggregate, the "Term Notes"),
(ii) Nonnegotiable Subordinated Daily Notes, Series 2005 (the "Daily Notes") and
(iii) Nonnegotiable Subordinated Special Daily Notes, Series 2005 (the "Special
Daily Notes") (the Term Notes, the Daily Notes and the Special Daily Notes are
collectively referred to herein as the "Securities") to be issued under an
Indenture, dated as of January ___, 2005, by and among the Company, as Issuer,
FNB, as Guarantor, and J.P. Morgan Trust Company, National Association, as
Trustee (the "Trustee") (as amended or supplemented from time to time, the
"Indenture"). Pursuant to a Guaranty dated as of January ___, 2005 (the
"Guaranty"), FNB will fully and unconditionally guaranty the Company's
obligations under the Securities.

      In connection with the foregoing, I have examined:

      a.    The Registration Statement and the exhibits thereto;

      b.    The Company's Certificate of Limited Partnership and the Partnership
            Agreement;

      c.    FNB's Articles of Incorporation and Bylaws;

      d.    The Indenture;

      e.    The form of General Partner Certificate setting forth the terms of
            the Term Notes, the Daily Notes and the Special Daily Notes;



      f.    The Guaranty; and

      g.    Such other records and documents as I have considered relevant,
            necessary or appropriate for purposes of this opinion; and

      I have also assumed:

            i)    The due authentication by or on behalf of the Trustee and the
                  due execution and delivery by the Company of the Securities;
                  and

            ii)   The issuance and sale of the Securities under the Indenture as
                  described in the Registration Statement, including receipt by
                  the Company of the full consideration for the Securities set
                  forth therein.

      Based upon such examination and assumptions, I am of the opinion that the
Securities will be enforceable obligations of the Company and the Guaranty will
be the enforceable obligation of FNB. The foregoing opinion is limited to the
laws of State of Delaware, the laws of the Commonwealth of Pennsylvania and the
federal laws of the United States.

      I consent to the use of my name in the Registration Statement under the
caption "Legal Matters" in the prospectus which constitutes part of the
Registration Statement and to the filing of this opinion as an exhibit to the
Registration Statement.

      This opinion is not to be reproduced, wholly or in part, or filed publicly
or used by any person without my prior written consent, nor shall it be used,
quoted, circulated or otherwise referred to for any other purpose.

                                                    Sincerely,

                                                    Charles C. Casalnova
                                                    Counsel