Classic studies have demonstrated that operating rooms are rife with communication and teamwork problems, and suboptimal teamwork has been linked to poor postoperative patient outcomes. In this rigorously designed study, surgical teams at 74 Veterans Affairs (VA) hospitals underwent teamwork training through the VA's Medical Team Training program. The training also included implementation of preoperative and postoperative checklists. The teamwork training was associated with a striking reduction in mortality compared to other VA hospitals that had not yet implemented the program, and a dose–response effect was also evident, with continuing training resulting in further reductions in mortality. An accompanying editorial lauds this study as an example of how to conduct a rigorous, evidence-based evaluation of a safety intervention, and stresses that addressing teamwork and safety culture are as essential to improving safety as technical and procedural interventions such as checklists.