Surgical checklists have provided some of the most profound recent improvements in patient safety. This study evaluated their usefulness in surgical crises, such as operating room cardiac arrests and massive hemorrhage. Although these critical surgical events are relatively common in large hospitals, they are rare for individual clinicians and result in the largest source of variation in surgical mortality among hospitals. Using high-fidelity simulations, surgical teams were randomized to handle the scenarios with or without checklists. Every team performed better when crisis checklists were available, and 97% of participants reported that they would want the checklist used if one of these crises happened while they were undergoing an operation. Atul Gawande (this study's senior author) describes the history and utility of checklists in his book, The Checklist Manifesto.