Takayasu's arteritis causes various arterial changes, including wall thickening, occlusion, aneurysm, and calcification. Similarly, Leriche's syndrome causes occlusion of the abdominal aorta or iliac arteries accompanied by ischemic symptoms of the distal lower extremities. Both diseases are potentially associated with the development of unexpected collateral arteries throughout the body. We evaluated whole body arteries in subjects with Takayasu's arteritis and Leriche's syndrome using 16-slice multislice CT and concluded that it was a useful tool to detect unexpected collateral arterial systems in Takayasu's arteritis or Leriche's syndrome in a non-invasive fashion.