Prior research suggests surgical safety checklists (SSCs) are associated with reductions in postoperative morbidity and mortality as well as improvement in teamwork and communication. These findings stem from evaluations of individual or small groups of hospitals. Studies with more hospitals have assessed the relationship of checklists with teamwork at a single point in time. The objective of this study was to evaluate the impact of a large-scale implementation of SSCs on staff perceptions of perioperative safety in the operating room.