In order to elucidate risk factors in arteriosclerosis obliterans (ASO), histories and physical and laboratory findings were reviewed in 163 patients with ASO, and the results were compared with ischemic heart disease (IHD) patients. Patients with ASO were much older and smoked more than patients with IHD. Such complications as hypertension, cerebrovascular disease were significantly more frequent in ASO patients than in IHD patients. On the other hand, the levels of serum total cholesterol, triglycerides, Apo A-II and Apo B were significantly lower in ASO patients than in IHD patients, although lipoprotein(a) tended to be higher in ASO. In ASO, remnant-like particles cholesterol tended to be higher when other presumable atherosclerotic risk factors were absent. The present results indicate that male gender, aging, smoking habit, hypertension and cerebrovascular disease are major risk factors in ASO patients. Although abnormal lipid metabolism may contribute to the development of ASO, we postulate that it plays a less significant role in IHD.