Background: Surveillance colonoscopy is required in patients with polyps due to an elevated colorectal cancer (CRC) risk; however, studies suggest substantial overuse and underuse of surveillance colonoscopy. The goal of this study was to characterize guideline adherence of surveillance recommendations after implementation of an electronic medical record (EMR)–based Colonoscopy Pathology Reporting and Clinical Decision Support System (CoRS). Methods: We performed a retrospective cohort study of patients who underwent colonoscopy with polypectomy at a safety-net healthcare system before (n=1,822) and after (n=1,320) implementation of CoRS in December 2013. Recommendations were classified as guideline-adherent or nonadherent according to the US Multi-Society Task Force on CRC. We defined surveillance recommendations shorter and longer than guideline recommendations as potential overuse and underuse, respectively. We used multivariable generalized linear mixed models to identify correlates of guideline-adherent recommendations. Results: The proportion of guideline-adherent surveillance recommendations was significantly higher post-CoRS than pre-CoRS (84.6% vs 77.4%; P<.001), with fewer recommendations for potential overuse and underuse. In the post-CoRS period, CoRS was used for 89.8% of cases and, compared with cases for which it was not used, was associated with a higher proportion of guideline-adherent recommendations (87.0% vs 63.4%; RR, 1.34; 95% CI, 1.23–1.42). In multivariable analysis, surveillance recommendations were also more likely to be guideline-adherent in patients with adenomas but less likely among those with fair bowel preparation and those with family history of CRC. Of 203 nonadherent recommendations, 70.4% were considered potential overuse, 20.2% potential underuse, and 9.4% were not provided surveillance recommendations. Conclusions: An EMR-based CoRS was widely used and significantly improved guideline adherence of surveillance recommendations.