Traumatic peripheral nerve lesions characteristically result in denervation muscular atrophy. Atrophy of disuse may take place concomitantly, either proximal, adjacent to or distal to the denervation muscular atrophy. The degree of atrophy of disuse depends upon the severity of the nerve lesion. Clinically, it is difficult to determine where true denervation muscular atrophy ends and accompanying atrophy of disuse begins. In such circumstances a clinician may be misled into belief that the cause of so apparently extensive a lesion is elsewhere. The patient then is often submitted to other complex diagnostic procedures and treatments. This difficulty can usually be dissipated by the use of electromyography, for each specific type of muscular atrophy produces its own characteristic electromyographic changes. Disuse atrophy produces no changes in electrical activity, whereas denervation atrophy manifests itself by typical denervation activity. Moreover it is possible to determine what part of muscular atrophy in a given area is owing to damage to a nerve and what part is owing only to disuse without denervation.