In chronic aorto-iliac occlusive disease, pre-existing renal artery stenosis may give rise to sufficient development of collateral blood flow and prevent ischaemic symptoms for a long time and therefore may cause delay in diagnosis. An early diagnosis of aorto-iliac disease is necessary in order to avoid fatal outcome. Duplex scanning is generally used to rule out a renal artery stenosis. This can generally detect the occlusion, but has some drawbacks such as obesity gas interposition, accessory renal arteries or the anatomy of the left renal artery, which may hinder complete examination of both renal arteries and may give rise to misdiagnosis. On the other hand, CT may provide detailed anatomic information.