Aneurysms are a common complication of arteriovenous grafts in hemodialysis patients, resulting from repetitive needle sticks in the graft material. Although aneurysms are thought to contribute to graft failure, there are no prospective studies evaluating their risk factors or impact on graft survival. The present study evaluated aneurysms in 117 hemodialysis outpatients with upper extremity grafts at a university-affiliated dialysis center. An arterial aneurysm was defined as a cannulation site defect diameter (difference between arterial cannulation site diameter and normal graft diameter) above the median value for the study population (0.63 cm). Subsequent graft outcomes were determined by retrospective analysis of a prospective vascular access database. Thrombosis-free graft survival was compared among patient subgroups using Cox proportional hazards models. Patients with an arterial aneurysm had significantly longer median graft age, when compared with those not having a aneurysm (888 vs. 588 days, p = 0.01). However, the two groups did not differ in patient age, sex, diabetes, body mass index, or graft location. The hazard ratio for graft thrombosis was 0.45 (95% confidence interval, 0.25-0.82, p = 0.009) for grafts with an arterial aneurysm, when compared with those without a defect (1-year graft survival of 71 vs. 50%). Graft age was not associated with the likelihood of graft thrombosis (p = 0.12). In contrast to the prevailing wisdom, arterial aneurysms are associated with improved graft survival.