Background and Purpose: The present study was performed to determine the relation between distribution of atherosclerosis and risk factors in Japanese patients with atherothrombotic occlusion. Methods: We studied 154 patients with atherothrombotic occlusion of the extracranial internal carotid artery (n=75, ICA group), the horizontal portion of the middle cerebral artery (n=47, MCA group), and the basilar artery (n=32, BA group), all of which were confirmed by cerebral angiography. We investigated the distribution of atherosclerosis of the three sites and compared the risk factors for atherosclerosis between the three groups. We used 113 subjects without stroke as the control group. Results: A strong correlation was present between atherosclerosis of the extracranial internal carotid artery and that of the basilar artery. However, only a weak correlation existed between atherosclerosis of the middle cerebral artery and that of the other vessels. Although the prevalence of smoking and hypertension was higher and high density lipoprotein cholesterol levels were lower in the three groups than in the control subjects, no significant differences were found in age, sex, prevalence of smoking and hypertension, serum levels of triglycerides, and high density lipoprotein cholesterol among the three groups. The prevalence of coronary heart disease and diabetes mellitus and the serum levels of hemoglobin A1c, total cholesterol, and low density lipoprotein cholesterol were higher in the ICA and BA groups than in the MCA group. The prevalence of electrocardiographic evidence of left ventricular hypertrophy was higher in the MCA group than in the other groups. Conclusions. In addition to smoking, hypertension, and low concentration of high density lipoprotein cholesterol, diabetes mellitus and hypercholesterolemia seem to be associated with atherosclerosis of the extracranial internal carotid artery and the basilar artery, and advanced hypertension may play a role in the development of middle cerebral artery occlusion.