Twenty patients with a clinically documented thoracic outlet syndrome were studied with regard to their clinical and electromyographic findings. Certain vascular as well as neurologic signs were noted to be prominent, particularly the presence of a supraclavicular bruit as well as reproduction of the patient's symptomatology while doing the thoracic outlet stress test. Other findings such as interossei weakness, ulnar nerve hypalgesia, supraclavicular tenderness to deep palpation, and reproduction of the patient's symptomatology via bilateral shoulder opposition were noted to be present. Classical maneuvers used to diagnose the thoracic outlet syndrome were compared and the thoracic outlet stress test was shown to be the best clinical test available at the present time. In addition, electromyographic studies were done showed abnormalities in only 55% of the cases when using multiple parameters that have been described in the literature recently. A new nerve conduction procedure was described here in which a conductions over the ulnar nerves were obtained in the thoracic outlet stress position and found, in a few cases, to show a reduction in amplitude of the evoked potential obtained at the hypothenar eminence. In addition, some findings suggestive of cervical radiculopathy were noted in the cases studied and several possible explanations for this were discussed.