Exhibit 5.1

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May 18, 2004



First Health Group Corp.
3200 Highland Avenue
Downers Grove, Illinois 60515

            Re:   Registration Statement on Form S-8 First Health Group Corp.

Ladies and Gentlemen:

      In connection with the preparation and filing by First Health Group Corp.
(the "Company") with the Securities and Exchange Commission under the Securities
Act of 1933, as amended, of a Registration Statement on Form S-8 (the
"Registration Statement") relating to the issuance by the Company of an
additional 1,500,000 shares (the "Additional Shares") of the Company's Common
Stock, par value $.01 per share, pursuant to the First Amended and Restated
First Health Group Corp. 2001 Directors' Stock Option Plan (as amended, restated
or otherwise modified, the "Plan"), you have requested our opinion with respect
to the matters set forth below.

      In our capacity as your counsel in connection with such registration, we
are familiar with the proceedings taken and proposed to be taken by the Company
in connection with the authorization, issuance and sale of the Additional
Shares, and for the purposes of this opinion, have assumed such proceedings will
be timely completed in the manner presently proposed. In addition, we have made
such legal and factual examinations and inquiries, including an examination of
originals or copies certified or otherwise identified to our satisfaction of
such documents, corporate records and instruments, as we have deemed necessary
or appropriate for purposes of this opinion.

      In our examination, we have assumed the genuineness of all signatures, the
authenticity of all documents submitted to us as originals, and the conformity
to authentic original documents of all documents submitted to us as copies.

      We are opining herein as to the effect on the subject transaction only of
the General Corporation Law of the State of Delaware, and we express no opinion
with respect to the applicability thereto, or the effect thereon, of the laws of
any other jurisdiction or, in the case of



MAY 18, 2004
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Delaware, any other laws, or as to any matters of municipal law or the laws of
any local agency within any state.

      Subject to the foregoing, it is our opinion that the Additional Shares
have been duly authorized and, when issued and sold upon exercise of the options
for such Additional Shares and payment of the exercise price therefor as
contemplated by the Plan, such Additional Shares will be validly issued, fully
paid and nonassessable.

      We consent to your filing this opinion as an exhibit to the Registration
Statement.

                                                    Very truly yours,

                                                    /s/ Latham & Watkins LLP

                                                    Latham & Watkins LLP