Purpose: To examine if the presence of large iliac arteries is a potential risk factor for the development of a type Ib endoleak (iliac sealing zone) or need for iliac artery-related secondary intervention in patients undergoing endovascular abdominal aortic aneurysm repair. Methods: The medical notes and all preoperative and postoperative plain abdominal radiographs and computer tomographic scans were reviewed for a consecutive series of 100 patients (89 men; mean age 75 years, range 56-91) with large iliac arteries (mean 19.7 mm, range 16-22) who had Zenith endovascular stent-grafts inserted for management of aortoiliac aneurysmal disease from January 1999 until September 2002. Endpoints were all-cause mortality, aneurysm-related death, endoleak, secondary intervention, secondary interventions, and stent-graft migration. Results: Mean follow-up was 30.1±8.3 months; at the last follow-up, 30% of patients were dead, 3% were aneurysm-related. Seven (7%) patients developed a type Ib endoleak, with the remainder being type II (29%), type Ia (2%), type III (1%), and type V (endotension, 1%). Eight (27.5%) type II endoleaks persisted, with the remainder closing spontaneously with sac shrinkage. The iliac artery-related secondary intervention rate was 10%, and the overall secondary intervention rate was 16%. Conclusion: Iliac arteries between 16 and 22 mm in diameter may be treated with a cuff to the iliac limb with an expectation of 90% efficacy. Surveillance is required, with a high index of suspicion for type 1b endoleaks. Early secondary iliac intervention with extension to the external iliac artery is recommended if there is an increase in sac size after 6 months.