Exhibit 5

March 25, 2002


Securities and Exchange Commission
450 Fifth Street N.W.
Washington, D.C. 20549

Re:      Arthur J. Gallagher & Co.
         Registration Statement on Form S-4

Gentlemen:

I am counsel for Arthur J. Gallagher & Co. (the "Company") in connection with
the above referenced Registration Statement on Form S-4 (the "Registration
Statement") relating to the registration for possible sale by the Company of
5,940,329 shares of the Company's common stock, par value $1.00 per share
("Common Stock"), in connection with future acquisitions (the Prospectus
included in the Registration Statement also relates to shares previously
registered on the Company's Registration Statements Nos. 333-75197 and
333-55254).

In this connection, I have examined the originals or copies identified to my
satisfaction of such documents, corporate and other records, certificates, and
other papers as I deemed necessary to examine for purposes of this opinion.

Based upon such examination, I am of the opinion that the shares of Common Stock
which may be sold by the Company, upon payment of the purchase price therefor,
will be duly and legally authorized and issued, 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 me under "Validity of Common Stock" in the
Prospectus included in the Registration Statement.

Very truly yours,

/s/ John C. Rosengren
John C. Rosengren
Vice President and General Counsel