March 23, 1999 EXHIBIT 5 Securities and Exchange Commission Judiciary Plaza 450 Fifth Street, N.W. Washington, D.C. 20549-1004 Re: Northern Trust Corporation: Registration Statement on Form S-8 Regarding Registration of Additional Participations in The Northern Trust Company Thrift-Incentive Plan Ladies and Gentlemen: I am Executive Vice President and General Counsel of Northern Trust Corporation, a Delaware corporation (the "Corporation"), and have served in that capacity in connection with the Corporation's filing of a Registration Statement on Form S-8 (the "Registration Statement") with the Securities and Exchange Commission covering the registration of an additional $100,000,000 of participations in The Northern Trust Company Thrift-Incentive Plan (the "Plan") consisting of shares of common stock of the Corporation, $1.66 2/3 par value per share, including the associated Preferred Stock Purchase Rights (collectively, the "Stock"). In that connection, I have examined such documents and have made such factual and legal investigations as I have deemed necessary or appropriate for the purpose of this opinion. Based on the foregoing, it is my opinion that those shares of Stock covered by the Registration Statement that are issued in accordance with the terms of the Plan will be legally issued, fully paid and non-assessable. In addition, Northern Trust Corporation has submitted the Plan to the Internal Revenue Service and has made all changes required by the IRS in order to qualify the Plan and undertakes that it will do so in the future with respect to any amendments that could affect the Plan's qualification. I hereby consent to the filing of this opinion as Exhibit 5 to the Registration Statement. Very truly yours, /s/ Peter L. Rossiter --------------------- Peter L. Rossiter Executive Vice President and General Counsel