BACKGROUND: Studies of surgical outcomes can be confounded by operative complexity. Complexity is difficult to assess from claims data due to the absence of established measures, but information on additional procedures is typically available. We hypothesized that analyzing same-day procedures (SDPs) would provide a useful step toward including operative complexity in risk adjustment. STUDY DESIGN: Colon resections were identified in California, Florida, and New York (2008 to 2011). Same-day procedures were categorized using 6 definitions. In-hospital mortality and postoperative complications were examined. For all outcomes, we developed multivariable logistic regression models to measure the association between the SDP category and outcomes. RESULTS: Rates of SDP were 74.9% total, 69.5% surgical, 31.6% nonsurgical, 36.6% colon, 51.4% abdomen, and 34.3% other for the 215,041 colon resections examined. Mortality was associated with the inclusion of any SDP category in univariate (6.2% vs 1.7%; p < 0.001) and multivariable (odds ratio [OR] = 2.14; 95% CI, 1.99-2.30; p < 0.001) analysis. The association with mortality was high for nonsurgical (OR = 2.36; 95% CI, 2.26-2.46) and other (OR = 2.33; 95% CI, 2.23-2.43) procedures and moderate for surgical (OR = 1.45; 95% CI, 1.37-1.54) and colon (OR = 1.51; 95% CI, 1.44-1.57) procedures, but abdominal procedures were not independently associated with mortality (OR = 1.01; 95% CI, 0.97-1.06). The total number of SDPs was also associated with higher complication rates. CONCLUSIONS: The risk of complications and mortality associated with colectomy was increased among patients with SDPs and the magnitude of the association was dependent on the type and quantity of additional procedures. Information on SDPs might reflect a component of operative risk not typically captured and should be considered as a candidate variable for risk adjustment when using claims to compare outcomes across large cohorts.