Differences in damage formation during fatigue crack propagation in acrylonitrile-butadiene-styrene polymer, between tests both fulfilling and not fulfilling linear elastic fracture mechanics requirements, were related to differences in crack propagation behaviour through the crack layer (CL theory. At both test conditions, damage consisted of crazing and shear yielding of the matrix, as well as elongation of rubbery domains. For a given crack length, the lower load level showed a higher intensity of craze damage. CL analysis showed that the process-dependent dissipation coefficient, β, is inversely proportional to the lifetime. Further, despite drastic differences in the amounts of each damage species, both tests were estimated to have the same specific enthalpy of damage (γ*=105 cal g−1), a material constant that is a measure of the intrinsic resistance to damage formation at the crack tip.