33 patients with angiographically confirmed dissection of the internal carotid artery (ICA) were followed prospectively. Cardinal symptoms were: 1) focal disturbances of the cerebral circulation (n = 28); 2) unilateral headache or neck pain (n = 20); 3) incomplete Horner's syndrome (n = 9). Neurological deficits without pain or sympathetic nerve damage developed in 11 patients. All patients had abnormal Doppler ultrasound findings over the ICA; in 22 there were markedly reduced flow velocities and retrograde flow components ("to- and- fro" phenomenon), typical of carotid artery dissection. During a mean observation time of 6.9 +/- 5.7 months serial Doppler ultrasound and angiographic examinations demonstrated recanalization in 73% after an average of 56 days. Angiographically different types (long segments in 13; pseudo-occlusions in 7; pseudoaneurysms in 5; and distal stenoses in 6; others in 2) are interpreted as expressions of different stages in the development of dissection up to complete recanalization.