Surgeons' technical skills are associated with surgical patient outcomes. This evaluation of an educational simulation intervention found that training procedural skills measurably but variably improved surgical performance. Increased experience with procedures following the training led to residents retaining these skills for up to 18 months. These results demonstrate the critical role of procedure volume in building surgical skill and safety. A related editorial focuses on the subset of learners who did not meet technical proficiency, among whom patient safety problems could occur.