A 59-year-old man was admitted to our hospital with numbness and calf claudication of the right leg. The enhanced CT scan and angiography revealed that the right internal iliac artery was unusually large caliber and distributed laterally, forming an aneurysm about 2.5cm in diameter. The right external iliac and femoral arteries were hypoplastic, and the superficial femoral artery terminated in several small branches, one of which coursed down to the lower leg as a saphenous artery. These findings established the diagnosis of a complete type persistent sciatic artery (PSA) with associated aneurysm. An excision of the sciatic artery with a right femoral-to-above-knee popliteal artery bypass grafting was performed. The PSA aneurysm is a rare vascular condition that can be successfully treated with reconstructive techniques if the diagnosis is correctly established.