We studied a consecutive series of 58 patients with penetrating missile injuries of the brachial plexus to establish the indications for exploration and review the results of operation. At a mean of 17 weeks after the initial injury, 51 patients were operated on for known or suspected vascular injury (16), severe persistent pain (35) or complete loss of function in the distribution of one or more elements of the brachial plexus (51). Repair of the nerve and vascular lesions abolished, or significantly relieved, severe pain in 33 patients (94%). Of the 36 patients who underwent nerve graft of one or more elements of the plexus, good or useful results were obtained in 26 (72%). Poor results were observed after repairs of the medial cord and ulnar nerve, and in patients with associated injury of the spinal cord. Neurolysis of lesions in continuity produced good or useful results in 21 of 23 patients (91%). We consider that a vigorous approach is justified in the treatment of penetrating missile injury of the brachial plexus. Primary intervention is mandatory when there is evidence of a vascular lesion. Worthwhile results can be achieved with early secondary intervention in patients with debilitating pain, failure to progress and progression of the lesion while under observation. There is cause for optimism in nerve repair, particularly of the roots C5, C6 and C7 and of the lateral and posterior cords, but the prognosis for complete lesions of the plexus associated with damage to the cervical spinal cord is particularly poor.