PROJECT SUMMARY/ABSTRACT Adverse cardiometabolic profiles and health behaviors often begin to emerge in adolescence. The following NHLBI Supplement Application outlines the proposal by the Adolescent Brain Cognitive Development (ABCD) Study to augment the current data being collected on this cohort with information about the cardiometabolic and hematologic health of youth during this time period. This additional data will include heart rate and blood pressure, total cholesterol, HDL, HbA1C, CBC, ferritin, iron, and child nutrition. These data will provide key information regarding the physiologic health of youth participating in ABCD and can be correlated with other data on cognitive functioning and brain development. Furthermore, examining the relationship between these physiologic outcomes and social and environmental exposures as well as lifestyle behaviors may help to estimate their impact on adolescent health and identify targets for intervention. ABCD’s large sample size (N=11,880) and diverse population will also enable researchers to develop a more nuanced understanding of these relationships as they pertain to different sociodemographic populations. The data elements to be collected in this supplement will be overseen by the ABCD Physical Health Assessment Workgroup with input from NHLBI. The project will also add ABCD investigators with expertise in these areas to oversee these aspects of the study and ensure scientific integration of analyses addressing several key questions. This group of investigators will join the Physical Health Assessment Workgroup and review the quality of the data collected and make recommendations regarding the collection of future waves of data collection. The Coordinating Center’s data management group (DAIRC) will assist with capturing and monitoring the data. They will also work with the site monitors and research coordinators/assistants at each of the 21 sites to ensure that they receive the training needed to faithfully and accurately implement the designed protocols. Overall, the information gained as part of the supplement will contribute to the open science ABCD data repository, enabling researchers to better understand the connections between physiologic biomarkers, cognitive function, and brain development.