Background: Because operating room crises are rare events, failure to adhere to critical management steps is common. We sought to develop and pilot a tool to improve adherence to lifesaving measures during operating room crises. Study Design: We identified 12 of the most frequently occurring operating room crises and corresponding evidence-based metrics of essential care for each (46 total process measures). We developed checklists for each crisis based on a previously defined method, which included literature review, multidisciplinary expert consultation, and simulation. After development, 2 operating room teams (11 participants) were each exposed to 8 simulations with random assignment to checklist use or working from memory alone. Each team managed 4 simulations with a checklist available and 4 without. One of the primary outcomes measured through video review was failure to adhere to essential processes of care. Participants were surveyed for perceptions of checklist use and realism of the scenarios. Results: Checklist use resulted in a 6-fold reduction in failure of adherence to critical steps in management for 8 scenarios with 2 pilot teams. These results held in multivariate analysis accounting for clustering within teams and adjusting for learning or fatigue effects (11 of 46 failures without the checklist vs 2 of 46 failures with the checklist; adjusted relative risk = 0.15, 95% CI, 0.040.60; p = 0.007). All participants rated the overall quality of the checklists and scenarios to be higher than average or excellent. Conclusions: Checklist use can improve safety and management in operating room crises. These findings warrant broader evaluation, including in clinical settings. © 2011 American College of Surgeons.