During a 4-year-period, 5 cases of ureteral obstruction by aorto-iliac aneurysm were detected. Over the same period 50 aorto-iliac aneurysms were resected. One of the 5 patients was not operated on. In the remaining 4, the aneurysm was resected and replaced by a Dacron bifurcation graft. Nephrectomy was performed in the first 2 patients. Autotransplantation of the remaining kidney was carried out in one case following enucleation of a hypernephroma ex vivo. In the other 2 patients, ureterolysis and intraperitoneal transposition of the ureter was performed in conjunction with resection of the aneurysm. One of the latter patients suffered from uraemia due to a non-functioning kidney on the other side. Ureteral obstruction appears to be a relatively common complication of aorto-iliac aneurysm. Elective evaluation of patients with aortic aneurysms should include late aortograms visualizing the ureters.