Arterial fibrodysplastic lesions involving the extracranial internal carotid and vertebral arteries were encountered among 15 women ranging in age from 21 to 79. Concomitant renal artery dysplasia was noted in five patients, including three with associated lesions involving the celiac or superior mesenteric vessels. Multiple intracranial aneurysms were found in seven patients. Rupture of these aneurysms with subarachnoid hemorrhage occurred in four patients and was the cause of death in three. Cerebral ischemic symptoms in certain instances may result from extracranial cerebrovascular fibrodysplasia. Considerable caution was used in selection of patients for surgery. Graduated intraluminal dilation of the internal carotid artery was performed on five occasions in this series. The pathogenesis of this disease is unknown. Hormonal influences and traction-stretch stresses to the vascular wall are implicated in the evolution of fibrodysplastic carotid and vertebral artery lesions.