Stretch injuries to peripheral nerves are often associated with poor recovery, which may relate to both the character and the extent of structural alterations in the nerve trunk. Previous biomechanical studies have provided insight into such structural changes; however most of these investigations have involved the testing of specimens after removal from the body. This investigation presents an in vivo model of nerve stretch injury and correlates functional recovery with different regions of the stress-strain relationship described in previous biomechanical studies. Functional recovery was measured for 8 weeks using the Sciatic Functional Index of de Medinaceli. Nerves stretched prior to reaching mechanical failure demonstrated excellent recovery within 2 to 3 weeks, with acute histologic features including variable amounts of degenerating axons. Nerves stretched through the point of mechanical failure were permanently deformed, with widespread degeneration and ruptures in the epineurium and perineurium. Despite these severe pathologic changes, a significant degree of recovery was observed by the end of the study period. These results suggest that if continuity is preserved, a substantial amount of recovery is possible following severe nerve stretch lesions in the rat. Preservation of continuity may create an optimal alignment for regenerating neurons.