An opportunity to study cerebrovascular changes in sickle cell anemia (SCA) presented itself when a black child with this disorder died of bihemispheric strokes. Angiography demonstrated severe occlusive vascular disease involving primarily the circle of Willis and major bifurcations of both internal carotid arteries. Collateral circulation to the distal branches of the internal carotid arteries occurred through transdural anastomoses from the external carotid system and via the leptomeningeal route. Perfusion of the basal ganglia was accomplished by vessels arising from the proximal internal carotid arteries. These changes resembled those of Moyamoya disease. Autopsy showed old and recent cerebral infarcts. Two vascular processes were responsible for the arterial occlusions: (1) exuberant intimal hyperplasia, and (2) old and recent thrombi with partial recanalization. The former has been described only once before in SCA. Small vessels in the basal ganglia were exceptionally numerous and dilated. We conclude that intimal hyperplasia within large cerebral arteries may be responsible for infarction and small vessel prliferation in basal ganglia in patients with SCA.