We retrospectively reviewed a prospectively collected breast center database to identify all patients with breast cancer undergoing surgery in a single center during a 9-year period ending 1 January 2010. Patients were divided into 2 groups based on whether surgery residents completed more than 50% of the critical portions of the case (Resident group) or not. The outcomes of operation length, reoperative rates, morbidity, and the long-term outcomes of cancer recurrence were compared by group