['Three competing goals at academic medical centers are to increase efficiency, to optimize clinical care, and to train residents. The goal of this project was to compare day surgery operating room (OR) efficiency measures for anesthesiologists working alone, working with residents, and working with certified nurse anesthetists in a tertiary multisubspecialty teaching hospital to determine if trainees significantly impact OR efficiency.', 'We retrospectively evaluated operating room times data for 2,427\xa0day surgery cases, comparing first case on-time starts, anesthesia-controlled times, induction times, emergence times, and turnover times for the 3 anesthesiologist groups.', 'Compared to the solo anesthesiologist group, anesthesiologists working with residents had significantly longer induction, emergence, and total anesthesia-controlled times (20.2\xa0±\xa08.0 vs 18.4\xa0±\xa07.0\xa0minutes). However, the anesthesiologists working with residents had more on-time starts (65% vs 53%) and lower turnover times 47.3\xa0±\xa013.6 vs 50.8\xa0±\xa014.5\xa0minutes) than the solo anesthesiologist group.'] Does presence of anesthesia resident trainees in day surgery unit have mixed effects on operating room efficiency measures?