Aorto-iliac aneurysms produce ureteric obstrucation by different mechanisms: deviation, compression and, above all, encirclement by peri-aneurysmal fibrosis. Whilst it is rare to find this as the cause for apparently primary ureteric obstruction, individuals with aorto-iliac aneumrysms quite often show evidence of ureteral abnormalities. The two cases presented illustrate these two possibilities. Routine pre-operative urography, or seven better a urographic phase of arteriography, is therefore suggested.