On the basis of a prospective study of 104 patients, the authors discuss the diagnostic value of the clinical symptoms revealing the thoracic outlet syndrome (TOS), as well as the specificity of the vascular functional exploration carried out to establish the diagnosis. Non-systematized pain and dysesthesia in the upper limb, with a postural or nocturnal onset, and Raynaud's sign are the most frequently observed signs. The "candlestick" maneuver still is the most reliable clinical triggering maneuver. The clinical features and the vascular functional explorations (capillaroscopy and digital plethysmography) allow demonstrating the existence of a true Raynaud's syndrome secondary to the TOS. The results of the arterial Doppler study distinguish the symptomatic and asymptomatic sides in the same patient, though without any correlation with the symptoms observed. The Doppler examination therefore seems to be reliable to demonstrate an anatomical duct, but remains insufficient to establish a causal relationship with the signal symptoms in most cases.