Forty-three patients with angiographically demonstrated complete occlusion of at least one internal or common carotid artery were compared with a sex and age matched control group with less than 60% occlusion of any single artery. The 100% group had a more severe initial insult, but posthospitalization cerebrovascular events were significantly less frequent. Ambulation, language, cerebral blood flow and metabolism, mean arterial blood pressure, mortality, functional independence, and intercurrent illnesses were not substantially different. The results of this study and others indicate that in patients with cerebrovascular disease clinical events are not quantitatively related to the degree of obstruction of the major arteries supplying the brain.