Nerve injuries associated with inversion sprains of the ankle have been mentioned in the literature on a case presentation basis only. Sixty-six consecutive patients with Grade II (30) and Grade III (36) ankle sprains were examined by electromyography 2 weeks after injury to determine the presence and distribution of nerve injuries. Ankle active range of motion (AROM) and the number of weeks postinjury when the patient could heel/toe walk and return to full activity were also noted. Five patients (17%) with Grade II sprains had mild peroneal nerve injury and three (10%) injured the tibial nerve. Clinical measurements were normal by the end of the second week. Thirty-one patients (86%) with Grade III sprains injured their peroneal nerve, while 30 (83%) incurred posterior tibial nerve injury. Ankle AROM was impaired, and heel/toe walking (5.1 weeks) and return to full activity (5.3 weeks) were markedly prolonged. The likely cause of this injury is considered to be a mild nerve traction or a hematoma in the epineural sheath at the bifurcation of the sciatic nerve into peroneal and posterior tibial branches. This report indicates that a consistently high percentage of patients with Grade III ankle sprains sustain a significant injury to both motor nerves in the leg and that rehabilitation time is markedly prolonged.