Background Adrenalectomy is a complex procedure performed in many settings, with and without residents and fellows. Patients often ask, "Will trainees be participating in my operation?" and seek reassurance that their care will not be adversely affected. The purpose of this study was to determine the association between trainee participation and adrenalectomy perioperative outcomes. Study Design We performed a cohort study of patients who underwent adrenalectomy from the 2005 to 2011 American College of Surgeons NSQIP database. Trainee participation was classified as none, resident, or fellow, based on postgraduate year of the assisting surgeon. Associations between trainee participation and outcomes were determined via multivariate linear and logistic regression. Results Of 3,694 adrenalectomies, 732 (19.8%) were performed by an attending surgeon with no trainee, 2,315 (62.7%) involved a resident, and 647 (17.5%) involved a fellow. The participation of fellows was associated with fewer serious complications (7.9% with no trainee, 6.0% with residents, and 2.8% with fellows; p < 0.001). In a multivariate model, the odds of serious 30-day morbidity were lower when attending surgeons operated with residents (odds ratio = 0.63; 95% CI, 0.45-0.89). Fellow participation was associated with significantly lower odds of overall (odds ratio = 0.51; 95% CI, 0.32-0.82) and serious (odds ratio = 0.31; 95% CI, 0.17-0.57) morbidity. There was no significant association between trainee participation and 30-day mortality. Conclusions In this analysis of multi-institutional data, the participation of residents and fellows was associated with decreased odds of perioperative adrenalectomy complications. Attending surgeons performing adrenalectomies with trainee assistance should reassure patients of the equivalent or superior care they are receiving. © 2014 by the American College of Surgeons.