An analytic expression in closed form is given for “fatigue,” the dependence of P(N), the switched charge per unit area P versus switching event number N, in ABO3 perovskite structure ferroelectric thin films is given. The analysis is based upon Arlt’s model for fatigue in bulk perovskites, which involves preferential electromigration of oxygen vacancies to sites parallel to the electrode–ferroelectric interface plane, together with some arguments by Brennan on the effectiveness of such defect planes in pinning domain walls. The model is applied to PZT/Pt with no adjustable parameters and yields in complete agreement with experimental data the dependence of P(N) at different frequencies, different voltages, and different temperatures. Notably, unlike other proposals in the literature, the model does not involve any charge injection from the electrodes. © 2000 American Institute of Physics.