A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was: is there a difference in cardiothoracic surgery outcomes in terms of morbidity or mortality of patients operated on by a sleep-deprived surgeon compared with those operated by a non-sleep-deprived surgeon? Reported search criteria yielded 77 papers, of which 15 were deemed to represent the best evidence on the topic. Three studies directly related to cardiothoracic surgery and 12 studies related to non-cardiothoracic surgery. Recommendations are based on 18 121 cardiothoracic patients and 214 666 non-cardiothoracic surgical patients. Different definitions of sleep deprivation were used in the studies, either reviewing surgeon's sleeping hours or out-of-hours operating. Surgical outcomes reviewed included: mortality rate, neurological, renal, pulmonary, infectious complications, length of stay, length of intensive care stay, cardiopulmonary bypass times and aortic-cross-clamp times. There were no significant differences in mortality or intraoperative complications in the groups of patients operated on by sleep-deprived versus non-sleep-deprived surgeons in cardiothoracic studies. One study showed a significant increase in the rate of septicaemia in patients operated on by severely sleep-deprived surgeons (3.6%) compared with the moderately sleep-deprived (0.9%) and non-sleep-deprived groups (0.8%) (P = 0.03). In the non-cardiothoracic studies, 7 of the 12 studies demonstrated statistically significant higher reoperation rate in trauma cases (P <0.02) and kidney transplants (night = 16.8% vs day = 6.4%, P <0.01), as well as higher overall mortality (P = 0.028) and morbidity (P <0.0001). There is little direct evidence in the literature demonstrating the effect of sleep deprivation in cardiothoracic surgeons on morbidity or mortality. However, overall the non-cardiothoracic studies have demonstrated that operative time and sleep deprivation can have a significant impact on overall morbidity and mortality. It is likely that other confounding factors concomitantly affect outcomes in out-of-hours surgery.