Background: Although the training of surgical residents is often considered in national policy addressing complications and safety, the influence of resident intraoperative involvement on surgical outcomes has not been well studied. Study Design: We identified 607,683 surgical cases from 234 hospitals from the 2006 to 2009 American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP). Outcomes were compared by resident involvement for all general and vascular cases as well as for specific general surgical procedures. Results: After typical ACS NSQIP comorbidity risk adjustment and further adjustment for hospital teaching status and operative time in modeling, resident intraoperative involvement was associated with slightly increased morbidity when assessing overall general or vascular procedures (odds ratio [OR] 1.06; 95% CI 1.04 to 1.09), pancreatectomy or esophagectomy (OR 1.26; 95% CI 1.08 to 1.45), and colorectal resections (OR 1.15; 95% CI 1.09 to 1.22). In contrast, for mortality, resident intraoperative involvement was associated with reductions for overall general and vascular procedures (OR 0.91; 95% CI 0.84 to 0.99), colorectal resections (OR 0.88; 95% CI 0.78 to 0.99), and abdominal aortic aneurysm repair (OR 0.71; 95% CI 0.53 to 0.95). Results were moderated somewhat after hierarchical modeling was performed to account for hospital-level variation, with mortality results no longer reaching significance (overall morbidity OR 1.07; 95% CI 1.03 to 1.10, overall mortality OR 0.97; 95% CI 0.90 to 1.05). Based on risk-adjusted event rates, resident intraoperative involvement is associated with approximately 6.1 additional morbidity events but 1.4 fewer deaths per 1,000 general and vascular surgery procedures. Conclusions: Resident intraoperative participation is associated with slightly higher morbidity rates but slightly decreased mortality rates across a variety of procedures and is minimized further after taking into account hospital-level variation. These clinically small effects may serve to reassure patients and others that resident involvement in surgical care is safe and possibly protective with regard to mortality.