ABSTRACT: Importance:Enhanced recovery protocols (ERPs) are standardized care plans of best practices that can decrease morbidity and length of stay (LOS). However, many hospitals need help with implementation. The Enhanced Recovery in National Surgical Quality Improvement Program (ERIN) pilot was designed to support ERP implementation. Objective:To evaluate the association of the ERIN pilot with LOS after colectomy. Design, Setting, and Participants:Using a difference-in-differences design, pilot LOS before and after ERP implementation was compared with matched controls in a hierarchical model, adjusting for case mix and random effects of hospitals and matched pairs. The setting was 15 hospitals of varied size and academic status from the National Surgical Quality Improvement Program. Preimplementation and postimplementation colectomy cases (July 1, 2013, to December 31, 2015) were collected using novel ERIN variables. Emergency and septic cases were excluded. A propensity score match identified a 2:1 control cohort of patients undergoing colectomy at non-ERIN hospitals. Interventions:Pilot hospitals developed and implemented ERPs that included expert guidance, multidisciplinary teams, data audits, and opportunities for collaboration. Main Outcomes and Measures:The primary outcome was LOS, and the secondary outcome was serious morbidity or mortality composite. Results:There were 4975 colectomies performed by 15 ERIN pilot hospitals (3437 before implementation and 1538 after implementation) compared with a control cohort of 9950 colectomies (4726 before implementation and 5224 after implementation). The mean LOS decreased by 1.7 days in the pilot (6.9 [interquartile range (IQR), 4-8] days before implementation vs 5.2 [IQR, 3-6] days after implementation, P < .001) compared with 0.4 day in controls (6.4 [IQR, 4-7] days before implementation vs 6.0 [IQR, 3-7] days after implementation, P < .001). Readmission did not differ pre-post for the pilot or controls. Serious morbidity or mortality decreased for pilot participants (485 [14.1%] before implementation vs 162 [10.5%] after implementation, P < .001), with no difference in controls, and remained significant after risk adjustment (adjusted odds ratio, 0.76; 95% CI, 0.60-0.96). After adjusting for differences in case mix and for clustering in hospitals and matched pairs, the adjusted difference-in-differences model demonstrated a decrease in LOS by 1.1 days in the pilot over controls (P < .001). Conclusions and Relevance:Participating ERIN pilot hospitals achieved shorter LOS and decreased complications after elective colectomy, without increasing readmissions. The ability to implement ERPs across hospitals of varied size and resources is essential. Lessons from the ERIN pilot may inform efforts to scale this effective and evidence-based intervention.