Healthcare purchasers, represented by the Leapfrog Group, have attempted to set standards for "quality" of surgical care that include a minimum volume for each of five major surgical procedures, with the assumption that higher volumes in surgery bring better outcomes. The VA National Surgical Quality Improvement Program (NSQIP) is a validated, outcome-based program that prospectively collects clinical data on all major surgical operations in the VA, and builds validated risk-adjustment models that generate, for each hospital and each surgical specialty within a hospital, risk-adjusted outcomes expressed as O/E (observed to expected) ratios for 30-day mortality and morbidity. The O/E ratio has been validated as a reliable comparative measure of the quality of surgical care. Unlike retrospective studies that are based on administrative databases, NSQIP studies have failed to demonstrate a direct relationship between volume and risk-adjusted outcomes of surgery across various specialties. These studies have emphasized that the quality of systems of care was more important than volume in determining the overall quality of surgical care at an institution. High-volume hospitals could still deliver poor care in as much as low-volume hospitals could deliver good care. NSQIP studies have also underscored the major limitations of claims data and administrative databases in the provision of adequate risk-adjustment models that are crucial for volume-outcome studies. Therefore, volume should not be substituted for prospectively monitored and properly risk-adjusted outcomes as a comparative measure of the quality of surgical care.