To ascertain the correlation between arteriosclerosis obliterans (ASO) of the lower extremities and coronary artery disease (CAD), 69 patients with lower extremity ASO were observed. Based on clinical symptoms, the patients were categorized as group A: 52 with intermittent claudication and group B: 17 with angina pectoris. All patients underwent angiography of both lower extremities and the heart. Results were as follows: 1. In group A, 33 patients had significant coronary stenosis with single (16 cases), double (12 cases) and triple (five cases) vessel disease. Sixteen patients had histories of myocardial infarction and two had vasospastic angina. In group B, 15 patients had significant coronary stenosis with single (five cases), double (six cases) and triple (four cases) vessel disease including two cases involving the left main trunk. Six patients had histories of myocardial infarction and two had vasospastic angina. 2. Electrocardiography revealed that 37 patients in group A and 14 patients in group B had abnormal ECGs as abnormal Q waves and ST-T changes. However, 10 patients in group A and three patients in group B had significant coronary stenosis despite their normal ECGs. 3. According to the sites of stenotic lesions, all 69 patients with ASO were classified in four types; as diffuse, pelvic, ilio-femoral and femoral. The incidence of CAD did not differ among these four types. 4. In group A, 38 patients experienced revascularization of ASO; 36 cases by bypass grafting, and two by percutaneous transluminal angioplasty (PTA). Ten patients received cardiac revascularization including three cases with coronary artery bypass graft (CABG) and seven cases with percutaneous transluminal coronary angioplasty (PTCA). In group B, 13 patients received revascularization of ASO with bypass grafting. Eleven patients had coronary revascularization including seven cases with CABG and four cases with PTCA. 5. Fourteen of the 69 patients received revascularization for both ASO and CAD. In conclusion, there is a highly significant coincidence of CAD in patients with ASO, and CAD is often silent. These data indicate that routine coronary angiography is necessary for detecting and preventing CAD in all patients with ASO. Coronary artery revascularization, especially PTCA, can be indicated prior to lower extremity revascularization.