This prospective study evaluated 50 patients with thoracic outlet syndrome. Detailed history and pain scale evaluation preceded physical examination, which included provocative tests (positional and compressive) and sensory evaluation (baseline and postprovocative vibration thresholds and two-point discrimination). Only one patient had a positive nerve conduction study/electromyograph at the brachial plexus level. Thirty-two percent of the patients had a compressive anatomic abnormality as seen on a computed tomography scan. Ninety-four percent had positive provocative position and compression test results. Two-point discrimination was normal in 98%. Clinical assessment of thoracic outlet syndrome is best achieved by reproduction of symptoms with compression and positional provocative testing. Results of the majority of tests (nerve conduction studies/electromyographs, x-ray films, sensory tests) will be normal. Measurements of changes in sensory thresholds during provocation of symptoms may be useful.