We report about 5 iliac anastomotic false aneurysms that occurred in 4 patients 8 to 21 years (average 15.5 years) after aortoiliac prosthetic reconstruction. The diagnosis was not established at once because of atypical clinical signs, in spite of the constant presence of an abdominal pulsating mass. All patients were operated by portal excision and graft replacement. One patient, who had presented with a hypovolemic collapse due to an acute rupture, died. The incidence of iliac false aneurysms after aortoiliac reconstructions is underestimated because the clinical surveillance is not reliable. The analysis of the explorations that were proposed led to prefer computed tomography to ultrasonography and angiography. The period of occurrence of iliac false aneurysms ranges between 6 to 10 years in average after the first operation. We therefore propose to perform a systematic follow-up CT examination on the 5th postoperative year, then every 5 years, and to operate the iliac false aneurysms as soon as their diagnosis is made.