OBJECTIVE: To determine the effect of consultant surgeon sleep hours on patient outcomes in cardiac surgery. DESIGN: Prospective observational cohort study. SUBJECTS: Between January 2004 and December 2009, we prospectively collected sleep hours of 6 consultant surgeons, ranging in age from 32 to 55 years, working in a tertiary care academic institution. The prospective study cohort included all patients undergoing coronary artery bypass, valve, combined valve-coronary artery bypass, and aortic surgery. The predicted risk of death and/or any of 10 major complications was calculated using our institutional multivariable model, which was then compared with observed values. Additional prespecified analyses examined the interaction between surgeon age, sleep hours, and postoperative outcomes. This study had more than 90% power to detect a 4% (clinically important) difference in overall complication rates among groups. MAIN OUTCOME MEASURES: Complication and mortality rates in operations performed by surgeons with 0 to 3, 3 to 6, or more than 6 hours' sleep the evening prior to surgery. RESULTS: Of 4047 consecutive surgical procedures, 83 were performed by a consultant with 0 to 3 hours, 1595 with 3 to 6 hours, and 2369 with more than 6 hours of sleep. Rates of mortality (3 [3.6%], 44 [2.8%], and 80 [3.4%], respectively; P = .53) were similar in the 3 groups, as were the observed vs expected ratios of major complications (1.20, 0.95, and 1.07, respectively; P = .25). There was no significant interaction between surgeon age, hours of sleep, and occurrence of death or any of 10 major complications (P = .09). CONCLUSION: This well-powered prospective study showed no evidence that consultant surgeon sleep hours had an effect on postoperative outcomes.