Fifty-five patients with 72 aneurysms of the iliac vessels were evaluated retrospectively during a 12-year period (1972 to 1985). Atherosclerotic vascular disease was found in all aneurysms. Marked male predominance (5:1) and advanced age (mean 74.6 years) characterized this population group. Two thirds of them harbored multiple aneurysms and isolated aneurysms were found primarily to involve the internal iliac artery (12 of 18 patients). Although symptomatic presentation varied with anatomic location and presence of rupture, most patients were either asymptomatic (45%) or had such nonspecific complaints (11%) that diagnosis was often delayed or erroneous. A mass detected during abdominal, rectal, or vaginal examination was found in 39 patients (70%). Aneurysm size ranged from 2.5 to 18 cm (mean 5.5 cm) for the entire group. Internal iliac aneurysms tended to be larger (7.7 cm) yet demonstrated no increased risk of rupture, which was encountered in 33% of patients. Elective operative management was undertaken in 26 patients with a mortality rate of 11%. When repair had to be performed as an emergency procedure mortality increased to 33%. Aneurysm ligation, resection, or endoaneurysmorrhaphy coupled with graft interposition when necessary did not seem to influence patient survival. Eleven patients treated nonoperatively demonstrated enlargement in three, rupture in one, and progressive ureteral obstruction in one patient. Iliac aneurysms demonstrate expansile growth with eruptive and erosive complications and therefore should be managed aggressively under elective circumstances.