Abstract
Retrograde vertebral arterial flow can occur when the ipsilateral subclavian artery is occluded in its proximal portion, and considerable shunting of blood may occur from the cerebral circulation via the vertebral-basilar system. Surgical restoration is possible in a high percentage of cases of extracranial vascular occlusive disease. Three patients are described who had cerebrovascular insufficiency caused by proximal subclavian arterial obstruction.