It is generally accepted that the non-linear elastic response of tendon is attributed to the sequential uncrimping and stretching of collagen fibers. We propose that the failure mechanism of tendon can similarly be described by the sequential rupturing of individual collagen fibers. Based on these two concepts, we developed a microstructural model to describe the failure of tendon. This model was used to analyze the stress-strain response of irradiated and non-irradiated patellar tendon allografts. The model fit the date well and indicated irradiation-induced changes in the microstructure consistent with those reported in the literature. These results suggest that the microstructural model presented here may be a useful tool in assessing the failure response of tendons.