Both Ivanov's yield criterion and a modification are incorporated in a nonlinear finite element program for the analysis of imperfect thin steel plates. The computer program is applied to the collapse analysis of imperfect steel plates subject to uniaxial compression. The results obtained with the modified Ivanov yield criterion are shown to be in good agreement with solutions obtained using a 'volume integration' with von Mises' yield criterion. They are significantly superior to results previously obtained using either Ilyushin's approximate yield criterion or a modification to that yield criterion