EXHIBIT 5.1

                       [LETTERHEAD OF F.N.B. CORPORATION]

                                 March 4, 2002

F.N.B. Corporation
F.N.B. Center
2150 Goodlette Road North
Naples, Florida 34102

Ladies and Gentlemen:

         As Corporate Counsel of F.N.B. Corporation (the "Registrant"), I am
familiar with the preparation and filing of the Registrant's Registration
Statement on Form S-8, to be filed with the Securities and Exchange Commission
on or about March 4, 2002, pursuant to which the Registrant proposes to issue up
to 626,486 shares of its $0.01 par value common stock (the "Shares") upon the
exercise of certain options assumed by the Registrant in connection with the
Registrant's acquisition of Promistar Financial Corporation.

         I have examined, and am familiar with, the originals or copies,
certified or otherwise, of the documents, corporate records and other
instruments of the Registrant relating to the proposed issuance of the Shares
which I deem relevant and which form the basis of the opinion hereinafter set
forth.

         I am of the opinion that under the laws of the State of Florida, the
jurisdiction in which the Registrant is incorporated, upon the issuance of the
Shares pursuant to the aforesaid Registration Statement, the Shares when so
issued will be duly authorized, validly issued and outstanding, and will be
fully paid and non-assessable shares of the Registrant's common stock, and no
personal liability will attach to the holders of any of the shares of the
Registrant's common stock.

         This opinion letter is given solely as of the date hereof and is
limited to the matters expressly set forth herein. I hereby consent to the
reference to me in the prospectus of the Registrant constituting part of the
Registration Statement and to the inclusion of this letter as an exhibit to the
Registration Statement.

                                          Sincerely,

                                          /s/ James G. Orie
                                          -------------------------------------
                                          James G. Orie
                                          Corporate Counsel, F.N.B. Corporation