INTRODUCTION: Methodological heterogeneity and reporting bias complicate interpreting endodontic outcomes. Supported by the American Association of Endodontists and its Foundation, this study developed the Core Outcome Set in Endodontics (COS-ENDO) to standardize reporting for studies of nonsurgical root canal treatment/retreatment, surgical endodontics, vital pulp therapy, apexification, and regenerative endodontics. This article, part 3 of a 5-part series, focuses on COS-ENDO for surgical endodontics, while other parts address the remaining treatments. METHODS: Outcomes were identified through a scoping review, a qualitative study with patients, and a web-based survey of American Association of Endodontists practicing members. In a 2-round Delphi survey, clinicians, patients, and researchers rated outcomes on a 9-point scale. Ratings were assessed against consensus criteria, and a virtual meeting finalized COS-ENDO. RESULTS: Of the 97 invited participants to round 1, 77 registered, and 73 (24 academicians/researchers, 26 clinicians, and 23 patients or their parents/caregivers) assessed 46 outcomes, with 17 excluded. The remaining outcomes-7 achieving consensus for inclusion and 22 lacking consensus-advanced to round 2 for rerating by 70 participants. This resulted in 1 outcome achieving consensus for exclusion, 10 for inclusion, and 18 lacking consensus. In the final meeting, 16 participants finalized the COS-ENDO for surgical endodontics, including Tooth survival, Pain, Signs of infection, Radiographic evidence of periradicular healing, Success, Functional tooth, Need for further intervention, and Adverse events/Complications. CONCLUSIONS: COS-ENDO is an important step in standardizing outcome reporting in endodontics, ensuring consistent reporting and enhancing research utility. Further efforts are needed to establish optimal measurement methods.