Objective: Prior studies have reported improved clinical outcomes with higher surgeon volume, which is assumed to be a product of the surgeon's experience with the index operation. We hypothesized that composite surgeon volume is an important determinant of outcome. We tested this hypothesis by comparing the impact of operation-specific surgeon volume versus composite surgeon volume on surgical outcomes, using open abdominal aortic aneurysm (AAA) repair as the index operation. Methods: The Nationwide Inpatient Sample was analyzed to identify patients undergoing open AAA repairs for 2000 to 2008. Surgeons were stratified into deciles based on annual volume of open AAA repairs ("operation-specific volume") and overall volume of open vascular operations ("composite volume"). Composite volume was defined by the sum of several open vascular operations: carotid endarterectomy, aortobifemoral bypass, femoral-popliteal bypass, and femoral-tibial bypass. Multiple logistic regression analyses were used to examine the relationship between surgeon volume and in-hospital mortality for open AAA repair, adjusting for both patient and hospital characteristics. Results: Between 2000 and 2008, an estimated 111,533 (95% confidence interval [CI], 102,296-121,232) elective open AAA repairs were performed nationwide by 6,857 surgeons. The crude in-hospital mortality rate over the study period was 6.1% (95% CI, 5.6%-6.5%). The mean number of open AAA repairs performed annually was 2.4 operations per surgeon. The mean composite volume was 5.3 operations annually. As expected, in-hospital mortality for open AAA repair decreased with increasing volume of open AAA repairs performed by a surgeon. Mortality rates for the lowest and highest deciles of surgeon volume were 10.2% and 4.5%, respectively (P <.0001). A similar pattern was observed for composite surgeon volume, as the mortality rates for the lowest and highest deciles of composite volume were 9.8% and 4.8%, respectively (P <.0001). After adjusting for patient and hospital characteristics, increasing composite surgeon volume remained a significant predictor of lower in-hospital mortality for open AAA repair (odds ratio, 0.994; 95% CI,.992-.996; P <.0001), whereas increasing volume of AAA repairs per surgeon did not predict in-hospital deaths. Conclusions: The current study suggests that composite surgeon volumenot operation-specific volumeis a key determinant of in-hospital mortality for open AAA repair. This finding needs to be considered for future credentialing of surgeons.