Purpose : To assess the usefulness of three-dimensional spiral CT angiography in the diagnosis and as a guide for the treatment of arteriosclerosis obliterans of the lower extremity. Materials and Methods : During a recent one-year period, CTA and conventional angiography were performed in 12 patients with suspected ASO. From the upper margin of the third lumbar vertebral body to below the knee joint, helical CT scanning was performed 30-45 seconds after the injection of Ultravist 370(150-180ml) by a power injector at the rate of 2.5-3.0ml/sec via the antecubital vein. The resulting data were reformatted by SSD after reconstruction of 5mm intervals, and CTA was compared with CA for site and degree of stenotic or occlusive lesion. Results : On CTA and CA, twenty-three occlusive lesions above the tibioperoneal artery were detected in 12 patients. On CA, three mild seven moderate and eight severe stenoses were seen, as well as five occlusions. There were three cases of overgrading and three of undergrading. Overall diagnostic accuracy was 73.9%(17/23). Calcifications were detected on axial CT scanning in two of three underestimated lesions. Migration of the thrombi was noted in one case. Conclusion : CTA may be useful in the evaluation of the arteries of the lower extremities, and valuable in the planning and follow-up of treatment.