HYPOTHESIS To test our hypothesis that unplanned return to the operating room (OR) is a useful quality indicator, we examined how often and for what reasons patients go back to the OR in a broad-based general surgery practice. DESIGN AND SETTING Prospective cohort study at a rural tertiary care center. PATIENTS Consecutive series of 3044 patients undergoing general surgery procedures in the OR between September 1, 1998, and March 31, 2000. Information about all postoperative adverse events occurring before discharge or within 30 days (whichever was longer) was collected prospectively. Unplanned return to the OR was defined as any secondary procedure required for a complication resulting directly or indirectly from the index operation. MAIN OUTCOME MEASURES Unplanned return to the OR, mortality, and hospital charges. RESULTS Overall, 107 (3.5%) had an unplanned return to the OR. A relatively small number of inpatient procedures accounted for a disproportionate share of unplanned reoperations, including colon resection (18% of total reoperations), renal transplant (9%), gastric bypass (6%), and pancreatic resection (6%). As expected, hospital charges were markedly higher for patients with unplanned returns to the OR. Reoperation was also associated with higher mortality rates; statistically significant increases were noted for pancreatic resection (33% vs 3.7%; P =.04), esophagogastrectomy (100% vs 4.2%; P =.002), and laparoscopic Nissen fundoplication (50% vs 0%; P =.01). Overall, 91 reoperations (85%) were for complications occurring at the original surgical site, including those related to an anastomosis (n = 16), surgical wound (n = 21), infection (n = 16), bleeding (n = 12), and other (n = 26). CONCLUSIONS Unplanned returns to the OR occur across a broad spectrum of general surgical procedures and carry significant implications. Because they most often reflect problems related to the procedure itself, reoperation rates may be useful for monitoring quality across hospitals and for identifying opportunities for quality improvement locally.