THE OCCURRENCE of aneurysms and occlusion of arteries in the absence of changes classified as atherosclerosis has puzzled the vascular surgeon and physician alike. Too often these lesions have been casually examined and their genesis ascribed either to congenital deformity or atherosclerosis. Tissue from early lesions in young subjects is difficult to obtain, and is not sought for in young subjects dying of causes other than arterial disease. Recently, the lesion termed fibromuscular hyperplasia of the renal artery has attracted much attention, and tissue has become available for study because of its association with hypertension, particularly in young subjects. Because of this association, the nephrologist, the urologist, and the vascular surgeon have studied this lesion extensively, and it has been concluded that the changes are specific to the renal artery.1,2 A review of the literature for a description of lesions associated with obstruction and aneurysm formation in other arteries,