Exhibit 5.1

                                 October 8, 2004

Board of Directors
F.N.B. Corporation
One F.N.B. Boulevard
Hermitage, Pennsylvania  16148

      Re:  F.N.B. Corporation
           Registration Statement on Form S-8
           204,669 Shares of Common Stock

Ladies and Gentlemen:

      I am the Chief Legal Officer of F.N.B. Corporation (the "Company"), and I
am familiar with the proceedings taken by the Company in connection with the
preparation and filing with the Securities and Exchange Commission under the
Securities Act of 1933 of a registration statement on Form S-8 (the
"Registration Statement") relating to the proposed offering by the Company of up
to 204,669 shares (the "Shares") of Common Stock, $.01 par value, of the
Company, that are to be issued as a result of the Company's assumption of stock
options issued under the F.N.B. Corporation/Slippery Rock Financial Corporation
1997 Directors Stock Option Plan, as amended, and the F.N.B.
Corporation/Slippery Rock Financial Corporation 1997 Incentive Stock Option
Plan, as amended (the "Plans").

      As counsel to the Company, I have supervised all corporate proceedings in
connection with the preparation and filing of the Registration Statement. I have
also examined the Company's Articles of Incorporation and By-laws, as amended to
date, the corporate minutes and other proceedings and the records relating to
the Plans and the authorization and offering of the Shares, and such other
documents and matters of law as I have deemed necessary or appropriate in order
to render this opinion.

      Based upon the foregoing, it is my opinion that the Shares, when issued in
accordance with the terms and conditions of the Plans, will be duly authorized,
legally and validly issued and outstanding, fully paid and nonassessable.

      I hereby consent to the filing of this opinion as an Exhibit to the
Registration Statement and to the reference to my name under Item 5 of Part II
of the Registration Statement.

                                          Respectfully,

                                          /s/ James G. Orie
                                          James G. Orie, Esquire