In emergency departments (EDs), high medical acuity, incomplete information, and productivity pressures can contribute to preventable adverse events and near misses. Systems solutions have improved medication safety and team communication in EDs, but few interventions have meaningfully affected diagnostic and treatment errors. Investigators conducted a randomized controlled trial to evaluate the impact of ED physicians' cross-checking their diagnostic and treatment plans with another physician. Compared with standard care, patients whose physicians performed cross-checking were 40% less likely to experience a preventable adverse event or near miss. This study's design, large sample size, and ascertainment of patient-centered outcomes were particularly robust. A past WebM&M commentary and PSNet perspective examined other initiatives to improve emergency department safety.