We investigated in detail the state of internal iliac artery (IIA) aneurysms over the midterm after the exclusion procedure.From January 1990 to December 1998, 29 patients underwent the exclusion procedure for IIA aneurysms. The medical records of 27 survivors were retrospectively reviewed, and 30 excluded aneurysms of these patients were followed up with computed tomography scanning over the midterm.In the immediate postoperative period, 26 aneurysms were completely thrombosed, and four were incompletely thrombosed. In the midterm, 24 aneurysms were completely thrombosed (complete group), and six were incompletely thrombosed (incomplete group). No aneurysms expanded or ruptured during the follow-up period from 6 to 98 months (mean, 26 months). The size of the excluded aneurysm decreased in 22 of 24 aneurysms in the complete group, but no change in size was noted in the six aneurysms in the incomplete group. The preoperative size of the IIA aneurysm in the incomplete group was significantly larger than that in the complete group (P =.0047). The size of two aneurysms in the incomplete group was smaller than 3.0 cm. The aneurysms in the incomplete group extended significantly deep into the pelvis as compared with those in the complete group (P =.0008).The exclusion of IIA aneurysm did not reliably result in thrombosis of the aneurysm. For IIA aneurysms extending deeply into the pelvis, even if the size of the aneurysm is smaller than 3.0 cm, the exclusion procedure should not be performed.