We have measured ‘‘in situ’’ the stresses generated in polyimide films produced from the ethyl ester of benzophenone tetracarbolic acid and methylene dianiline during the curing cycle. The room temperature stress in a fully cured film (to 400 °C) is approximately 70 MPa. The stresses at room temperature vary with the cure temperature and are due to coefficient of thermal expansion mismatch between film and substrate. The in situ measurements show that the glass transition temperature is the same as the maximum cure temperature that the film experiences. The stress measurements were made using an x-ray double crystal lattice curvature technique.