In traumatic brachial plexus injuries a thorough neurological, electrodiagnostic, and radiological examination is essential to determine treatment and prognosis. The most important diagnostic question concerns the presence or absence of a preganglionic nerve root lesion. Electromyography and motor and sensory conduction studies were performed in 17 patients with traumatic plexus injuries who had myelographic evidence of nerve root avulsion; in 8 of these clinical and electrophysiological features confirmed the X-ray findings. However, in 9 cases there was a discrepancy between myelographic and neurophysiological data regarding the actual number and sites of roots avulsed. Thus, in 2 cases myelography showed avulsion of one more root than did conduction studies and EMG; in 2 others, there was discordance as to the specific roots avulsed; in 4 cases fewer nerve roots seem to be avulsed radiologically than predicted clinically, and in 1, none at all, although clinical and electrophysiological data were compatible with avulsion of four roots. In 6 cases recovery showed that avulsions indicated by clinical and electrophysiological considerations could not have occurred. When both EMG and myelography are misleading, surgical exploration should be considered.