When thin adhered films of a polyimide (Ciba-Geigy XU-293) on rigid substrates are immersed in xylene, defects, that look like cracks to the naked eye, are formed. These defects are caused by the presence of the combination of the equibiaxial tension in the film and the xylene. The stress comes from the solvent loss and the thermal expansion mismatch between the substrate and the film. The defects are found to be local deformation zones, showing considerable optical anisotropy and a microstructure strongly influenced by the adhesion condition to the substrate. Although they retain a smooth surface on the face in contact with the substrate in the bonded regions, the deformation zones release a significant amount of stress. The stress released is measured by a photoelastic technique and is found to be in excellent agreement with that calculated from the local thickness change assuming simple elasticity. These deformation zones grow at a speed that is independent of their length and initiation time but increase rapidly with film thickness from a threshold at a thickness of about 3 microns. The observed thickness effect can be explained by a fracture mechanics analysis of adhered films where, unlike the case in free films, the energy release rate, G, is independent of crack length but varies with film stress and linearly with film thickness.