['We evaluated effect of resident involvement on outcomes after laparoscopic and open colon resection for malignancy.', 'Patients undergoing colectomy were queried using the American College of Surgeons\' National Surgical Quality Improvement Program. "Attending alone" and "Resident" cohorts were compared with primary end point of overall morbidity.', 'Of 37,330 patients, residents were involved in 26,190 (70.2%) cases. Attending alone patients were older with higher vascular, cardiac, and pulmonary comorbidity. Univariate analysis demonstrated increased operative time (181.0 ± 98.4 vs 138.7 ± 77.0, P < .001), reoperation (5.7% vs 5.2%, P = .041), and readmission rates (11.9% vs 9.6%, P = .037) with resident involvement. Serious (16.0% vs 13.9%, P < .001), minor (17.5% vs 14.1%, P < .001), and overall morbidity (26.4% vs 22.5%, P < .001) were higher with resident participation. Mortality (2.0% vs 2.8%, P < .001) and failure to rescue (.8% vs 1.2%, P < .029) were lower with resident involvement. Resident involvement showed independent association with overall morbidity in both laparoscopic (odds ratio, 1.2; 95% confidence interval, 1.13 to 1.38, P < .001) and open cases (odds ratio 1.3, 95% confidence interval, 1.18 to 1.35, P < .001).'] Does surgical resident involvement differentially affect patient outcomes in laparoscopic and open colectomy for malignancy?