ALTHOUGH traumatic or surgical occlusion of one or both common carotid arteries or their branches may be asymptomatic, especially in young persons, spontaneous thrombosis of these vessels in a subject with marked vascular sclerosis is more likely to lead to serious neurologic disturbances. Recent experience with three patients having optic nerve atrophy accompanying proved spontaneous thrombosis of the carotid arteries has prompted this communication. The cause of spontaneous thrombosis of the carotid arteries is generally considered to be atherosclerosis. The thrombosis is commonly associated with sclerosis of the aorta and with aortic aneurysms. However, cases have been reported in which the cause of the thrombosis was thought to be obliterative syphilitic arteritis, embolism or nonsyphilitic arteritis. The recent reports of Galdston and associates,1 Wolfe,2 Erickson3 and Webster, Dolgoff and Gurdjian,4 (the last of which included two of the present cases) show that advanced atheromatous changes are