PROJECT SUMMARY/ABSTRACT Climate change-related extreme weather – extreme heat, heatwaves, and intense rainfall – pose an urgent threat to public health. Children may bear a disproportionate burden of the adverse effects of extreme weather for a multitude of reasons, including their immature and developing bodies, low body mass, and dependence on caregivers to respond to environmental threats. A growing body of literature, including studies from our own research group, shows links between extreme weather and acute childhood morbidity. Nevertheless, there remain critical knowledge gaps, including incomplete characterization of the scope of pediatric health outcomes related to weather extremes and almost no assessment of chronic health (lasting) impacts. We propose to conduct a large, multi-site study of the relationship between extreme weather and children’s health by linking data from PEDSnet – a research consortium of U.S. pediatric health systems, including over 12 million children, spanning the years 2009 through 2023 – with high-resolution geospatial measures of extreme weather and residential neighborhood environments. Specifically, we aim to: 1) Estimate associations of extreme weather events – hot temperatures, heatwaves, heavy rainfall, and intense rainstorms – with a broad scope of acute adverse health events in children, such as dehydration, asthma exacerbation, respiratory infections, acute gastroenteritis, injuries, and acute care for mental health disorders; 2) Investigate the relationship between cumulative exposure to multiple, possibly repeated extreme weather events, and development of chronic health conditions during childhood – including mental health disorders, asthma and allergic rhinitis, and overweight/obesity – assessing initial development of the condition, as well as its persistence; 3) Quantify disproportionate impacts of extreme weather on children according to small-area (census-tract) indicators of residential neighborhood-level social and infrastructural vulnerability. Our study will considerably advance scientific understanding of relationships between climate-change related weather extremes and children’s health. Given the geographical diversity of the study area, the size of the patient population included, the detailed richness of our compiled database, and the novel investigation of chronic health outcomes, this project will have a sustained impact on the state of knowledge about the scope, magnitude, and inequities of children’s health outcomes from extreme weather.