We introduce an interferometric method for measuring the profiles of cylindrical surfaces. A Fizeau interferometer with a flat reference is used to test part of a cylindrical surface, and various parts of the surface can be tested by the rotation of the surface. The algorithm for linking separate measurements is described, and testing examples for measuring sagitta over 3 mm of a cylindrical surface with an elliptical cross section are included. Measurement results show that repeatability for the above test to the order of 1 microm, is feasible.