EXHIBIT 5.1


                       FIRST HORIZON NATIONAL CORPORATION

                             Clyde A. Billings, Jr.
                             Senior Vice President,
                            Assistant General Counsel
                             and Corporate Secretary


March 17, 2005

Board of Directors
First Horizon National Corporation
165 Madison Avenue
Memphis, TN  38103

Ladies and Gentlemen:

I have acted as counsel  to First  Horizon  National  Corporation,  a  Tennessee
corporation  (the  "Company"),  in connection with the registration on Form S-8,
Registration  Statement (the "Registration  Statement") under the Securities Act
of 1933,  as amended  (the  "Act"),  of that  additional  1,000,000  shares (the
"Securities")  of common  stock,  par value  $0.625  per share,  of the  Company
("Common  Stock"),  and associated  stock  purchase  rights (the "Rights") to be
issued  pursuant to the  Shareholder  Protection  Rights  Agreement  dated as of
October  20,  1998  (the  "Rights  Agreement")  between  the  Company  and First
Tennessee Bank National  Association,  as Rights Agent (the "Rights Agent"). The
Securities  are to be issued to Plan  participants  pursuant to the terms of the
First Horizon  National  Corporation 2003 Equity  Compensation  Plan, as amended
(the "Plan").  The Securities are in addition to the 3,000,000  shares of Common
Stock  previously  registered  for issuance  under the Plan pursuant to Reg. No.
333-109862.  I have  examined the  originals  or copies,  certified or otherwise
identified to my satisfaction, of such corporate records, certificates and other
documents,  and  such  questions  of  law,  as I have  considered  necessary  or
appropriate for the purposes of this opinion.

Upon the basis of such  examination  and  subject to the  limitations  contained
herein, it is my opinion that:

     1. The Plan has been duly adopted.

     2. The  Securities,  being  1,000,000  shares of Common  Stock which may be
issued from authorized but unissued shares by the Company  pursuant to the Plan,
when issued by the Company  pursuant to the terms and  conditions of the Plan as
administered  by the Committee  authorized  thereunder,  will be validly issued,
fully paid, and non-assessable.

     3. When such Securities have been validly issued,  the Rights  attributable
to such Securities will be validly issued.  In rendering the foregoing opinion I
have assumed that,  prior to and at the time of the issuance of the  Securities,
the Rights will not have been  redeemed and the  Separation  Time (as defined in
the Rights Agreement) will not have occurred.




In  connection  with my opinion set forth in paragraph 3 above,  I note that the
question  whether the Board of  Directors  of the  Company  might be required to
redeem  the  Rights  at  some  future  time  will  depend  upon  the  facts  and
circumstances  existing  at that time and,  accordingly,  is beyond the scope of
such opinion.

The  foregoing  opinion is limited to the federal laws of the United  States and
the laws of the State of  Tennessee,  and I am  expressing  no opinion as to the
effect of the laws of any other jurisdiction.

In  rendering  the  foregoing  opinion,  I have relied to the extent I deem such
reliance  appropriate as to certain matters on statements,  representations  and
other information  obtained from public  officials,  officers of the Company and
other sources believed by me to be responsible.

I hereby consent to the filing of this opinion as an exhibit to the Registration
Statement,  and to the reference to me in the Registration  Statement. In giving
such consent,  I do not thereby admit that I am in the category of persons whose
consent is required under Section 7 of the Act.


Very truly yours,

/s/Clyde A. Billings, Jr.
-------------------------
  Clyde A. Billings, Jr.



                       First Horizon National Corporation
                      165 Madison Avenue, Memphis, TN 38103