BACKGROUND: Emergency information forms (EIFs) have been proposed to provide critical information for optimal care of children with medical complexity (CMC) during emergencies; however, their impact has not been studied. The objective of this study was to measure the impact and utility of EIFs in simulated scenarios of CMC during medical emergencies. METHODS: Twenty-four providers (12 junior, 12 experienced) performed 4 simulations of CMC, where access to an EIF was block randomized by group. Scenario-specific critical action checklists and consequential pathways were developed by content experts in simulation and pediatric subspecialists. Scenarios ended when all critical actions were completed or after 10 minutes, whichever came first. Two reviewers independently evaluated the videorecorded performances and calculated scenario-specific critical action scores. Performance in scenarios with and without an EIF was compared with Pearson's χ2 and Mann-Whitney U tests. Interrater reliability was assessed with intraclass correlation. Each provider rated the utility of EIFs via exit questionnaires. RESULTS: The median critical action score in scenarios with EIFs was 84.2% (95% confidence interval [CI], 71.7%-94.1%) versus 12.5% (95% CI, 10.5%-35.3%) in scenarios without an EIF (P < .001); time to completion of scenarios was shorter (6.9 minutes [interquartile range 5.8-10 minutes] vs 10 minutes), and complication rates were lower (30% [95% CI, 17.4%-46.3%] vs 100% [95% CI, 92.2%-100%]) with EIFs, independent of provider experience. Interrater reliability was excellent (intraclass correlation = 0.979). All providers strongly agreed that EIFs can improve clinical outcomes for CMC. CONCLUSIONS: Using simulated scenarios of CMC, providers' performance was superior with an EIF. Clinicians evaluated the utility of EIFs very highly.