We have analysed the results of repair of traumatic lesions of the musculocutaneous nerve in 85 patients, which were graded by Seddon's modification of the Medical Research Council system into three types of injury: open 'tidy', open 'untidy' and closed 'traction'. They were also correlated with associated arterial injury. There were 57 good, 17 fair and 11 poor results. The type of injury was the most important factor in determining the result; 12 of 13 open-tidy lesions gave good results compared with 30 of 48 closed-traction lesions. The results were better when the nerves were repaired within 14 days of injury and when grafts were less than 10 cm long. They were worse in the presence of associated arterial or bony injury.