The clinical, duplex, and angiographic findings in six patients with seven spontaneous extracranial carotid artery dissections are reported. Four dissections resulted in internal carotid artery occlusion. These patients complained of ipsilateral headache followed by contralateral hemiplegia. The other three dissections involved the common carotid artery and resulted in dual (one true and one false) lumens. Two of these dissections were asymptomatic. All dissections were treated nonoperatively with anticoagulant therapy. Neurologic deficits improved or disappeared in all symptomatic patients. On follow-up studies, one of the four internal carotid occlusions completely resolved with normalization of the duplex examination. All three dual lumen dissections remained patent on serial studies. Diagnostic duplex characteristics, both conclusive and supportive, of carotid dissections are described. Duplex scanning is shown to be accurate in diagnosing and ideally suited for serially following spontaneous carotid dissections.