Clinical and angiographic features and outcome in 25 patients with spontaneous dissections of the vertebral arteries are described. Most patients were in their fourth or fifth decade of life, and women predominated. Forty-eight percent of the patients were hypertensive. Angiographic evidence of fibromuscular dysplasia was noted in one only. Brainstem ischemic symptoms (usually a lateral medullary syndrome) and ipsilateral occipital headache and neck pain (often preceding but sometimes associated with or following the brainstem ischemic event) were the most common clinical findings. The angiographic features in decreasing order of frequency were luminal stenosis (often irregular and tapered), aneurysm, occlusion, and intimal flap. On follow-up, most of the patients (88%) made complete or very good recoveries. Angiographic abnormalities either subsided or improved in 76%. Multivessel dissection (involvement of both vertebral arteries or one or both vertebral arteries and one or both internal carotid arteries) was noted in about two-thirds of the patients. This tendency of vertebral artery dissections to involve multiple cervicocephalic vessels concurrently, if not simultaneously, implies that four-vessel angiography should be attempted if a vertebral artery dissection is visualized. It also raises the possibility of an underlying arteriopathy that predisposes the vessel to dissection.