The records of 50 patients with isolated iliac artery aneurysms seen between January 1970 and January 1982 were reviewed. Forty-seven were men and three were women. Their ages ranged from 41 to 92 years (mean 69.7 years). Aneurysm diameter ranged from 2 to 20 cm (mean 4.7 cm). Seventeen patients had multiple aneurysms. Sixty-two percent of aneurysms were on the right side. Eighty-nine percent were located in the common iliac artery, 10% in the internal iliac artery, and 1% in the external iliac artery. Twelve patients had symptoms; all presented with sudden pain. Rupture occurred in seven patients; only three patients survived. Twenty-four patients had surgical treatment. Aneurysmorrhaphy with graft interposition was the most common procedure. There were no deaths during elective operation. Nineteen patients who did not undergo operation were followed from 0.25 to 11 years (mean 4.9 years). Enlargement occurred in nine patients and rupture in one. We conclude that the natural history of isolated iliac artery aneurysms is similar to that of other atherosclerotic aneurysms. Elective resection and arterial reconstruction are recommended.