Importance  The association between physician fatigue and patient outcomes is important to understand but has been difficult to examine given methodological and data limitations. Surgeons frequently perform urgent procedures overnight and perform additional procedures the following day, which could adversely affect outcomes for those daytime operations.

Objective  To examine the association between an attending surgeon operating overnight and outcomes for operations performed by that surgeon the next day.

Design, Setting, and Participants  In this cross-sectional study, a retrospective analysis of a large multicenter registry of surgical procedures was done using a within-surgeon analysis to address confounding, with data from 20 high-volume US institutions. This study included 498 234 patients who underwent a surgical procedure during the day (between 7 am and 5 pm) between January 1, 2010, and August 30, 2020.

Exposures  Whether the attending surgeon for the current day’s procedures operated between 11 pm and 7 am the previous night. Two exposure measures were examined: whether the surgeon operated at all the previous night and the number of hours spent operating the previous night (including having performed no work at all).

Main Outcomes and Measures  The primary composite outcome was in-hospital death or major complication (sepsis, pneumonia, myocardial infarction, thromboembolic event, or stroke). Secondary outcomes included operation length and individual outcomes of death, major complications, and minor complications (surgical site infection or urinary tract infection).

Results  Among 498 234 daytime operations performed by 1131 surgeons, 13 098 (2.6%) involved an attending surgeon who operated the night before. The mean (SD) age of the patients who underwent an operation was 55.3 (16.4) years, and 264 740 (53.1%) were female. After adjusting for operation type, surgeon fixed effects, and observable patient characteristics (ie, age and comorbidities), the adjusted incidence of in-hospital death or major complications was 5.89% (95% CI, 5.41%-6.36%) among daytime operations when the attending surgeon operated the night before compared with 5.87% (95% CI, 5.85%-5.89%) among daytime operations when the same surgeon did not (absolute adjusted difference, 0.02%; 95% CI, −0.47% to 0.51%; P = .93). No significant associations were found between overnight work and secondary outcomes except for operation length. Operating the previous night was associated with a statistically significant decrease in length of daytime operations (adjusted length, 112.7 vs 117.4 minutes; adjusted difference, −4.7 minutes; 95% CI, −8.7 to −0.8, P = .02), although this difference is unlikely to be meaningful.

Conclusions and Relevance  The findings of this cross-sectional study suggest that operating overnight was not associated with worse outcomes for operations performed by surgeons the subsequent day. These results provide reassurance concerning the practice of having attending surgeons take overnight call and still perform operations the following morning.