Two cases, in siblings, of renovascular hypertension caused by fibromuscular dysplasia (FMD) of the renal artery associated with cerebral aneurysms are reported. Both of the cases were found to have cerebral aneurysm, as well as multiple stenotic or occluded lesions in arteries such as renal, mesenteric, celiac, and internal carotid arteries. One case died of subarachnoid hemorrhage and the other case was successfully operated on for the aneurysm. This report suggests that FMD should be considered to be a systemic angiopathy including the cerebral artery, as well as the renal artery. Thus, cerebral angiography is recommended to detect the association with cerebral aneurysm, at least, in cases with multiple lesions of FMD. Occurrence of FMD in siblings also indicates that a genetic factor might be involved in the pathogenesis of FMD.