Purpose: To assess early and midterm outcomes of iliac branch device (IBD) implantation without an aortic stent-graft for the treatment of isolated common iliac artery aneurysm (CIAA). Methods: From December 2006 to June 2016, 49 isolated CIAAs in 46 patients were treated solely with an IBD at 7 vascular centers. Five patients were lost to follow-up, leaving 41 male patients (mean age 72.5±7.8 years) for analysis. Mean CIAA diameter was 39.1±10.5 mm (range 25–65). Thirty-two patients (2 with bilateral CIAAs) were treated with a Cook Zenith iliac branch device; 9 patients (1 bilateral) received a Gore Excluder iliac branch endoprosthesis. Primary endpoints were technical success, survival, aneurysm exclusion, device patency, and freedom from reintervention at 1 and 5 years. Freedom from major adverse events and aneurysm shrinkage at 1 year were also assessed. Results: Thirty-day mortality and the IBD occlusion rate were 2.4% and 2.3%, respectively. At a mean follow-up of 40.2±33.9 months, no patient presented buttock claudication, erectile dysfunction, or bowel or spinal cord ischemia. Three patients died within 6 months after the procedure. Estimates of cumulative survival, device patency, and freedom from reintervention were 90.2%, 95.2%, and 95.7%, respectively, at 1 and 5 years. At 1 year, CIAA shrinkage ≥5 mm was recorded in 21 of 38 survivors. No evidence of endoleak, device migration, or disconnection was found on imaging follow-up. Conclusion: The use of IBDs without an aortic stent-graft for isolated CIAAs resulted in excellent patency, with low morbidity and mortality. This, in conjunction with no endoleak or migration and a low reintervention rate, supports the use of isolated IBDs as a stable and durable means of endovascular reconstruction in cases with suitable anatomy. Longer follow-up and a larger cohort are needed to validate these results.