OBJECTIVE The natural history of untreated major injuries is not well known, although serious complications are seen. The follow-up of patients who have trauma is often incomplete, and this study was undertaken to evaluate the nature of these wounds. METHODS Thirty-one patients with missed major arterial wounds were examined and treated according to the pathologic condition encountered. All had been seen at other hospitals, some on more than one occasion, and then sought assistance for continued problems. RESULTS There were 16 aneurysms in 31 patients: 4 arteriovenous fistulas, 4 dissections, 3 thromboemboli, and 1 stenosis. The arteries included the following: carotid 12, aorta 5, femoropopliteal 8, subclavian 2, axillary 1, innominate 1, iliac 1, and tibial 1. Three patients had a stroke, one had a transient ischemic attack, two had leg ischemia, and one had a gangrenous foot. Operation was required in 27 patients; there were no deaths. CONCLUSIONS Transmural traumatic arterial wounds of major vessels can result in serious delayed complications, months or even years after the injury. False aneurysms, dissections, occlusions, and fistulas in the extremities may not be lethal, but they cause significant disability. Such lesions in the neck or trunk are more dangerous. Despite the inconvenience and expense, patients with injuries of major arteries are best served by early repair of the wound.