PURPOSE: To report the results of preprocedural embolization of collateral branches arising from abdominal aortic aneurysms (AAA) scheduled for endovascular repair. METHODS: Twenty-three consecutive AAA patients (all men; mean age 73 years, range 56-82) had coil embolization of patent lumbar and inferior mesenteric arteries (IMA) in a staged procedure prior to endovascular repair. Embolization with microcoils was attempted in 37 of the 52 identified lumbar arteries and 14 of 15 inferior mesenteric arteries. Follow-up included biplanar abdominal radiography, spiral computed tomography, and duplex ultrasonography at 1, 30, 90, and 180 days after the stent-graft procedure and at 6-month intervals thereafter. RESULTS: Successful embolization was obtained in 24 (65%) of lumbar arteries, while all 14 (100%) IMAs were occluded with coils. No complication was associated with embolotherapy. Over a mean 17-month follow-up of 22 patients (1 intraoperative death), there was only 1 (4.5%) type II endoleak from a patent lumbar artery, with no sac expansion after 2 years. There were 4 (18%) type I and 1 (4.5%) type III endoleaks. CONCLUSIONS: The embolization of side branches arising from an infrarenal aortic aneurysm before endovascular repair is feasible, with a high success rate; this maneuver may play a relevant role in reducing the rate of type II endoleak, improving long-term outcome.