The study used administrative data to identify the social determinants that have the greatest impact on Medicaid expenditures in adolescence. Data were compiled using the Washington State Department of Social and Health Services Integrated Client Databases, which link data from state systems including Medicaid claims and social services receipt. Medical system and behavioral health service costs of over 180 000 Medicaid‐enrolled adolescents aged 12‐17 were measured using integrated administrative data from Washington State. Social determinants of health, including child maltreatment and parent risk factors, were also measured. Two‐stage regression models were used to identify factors associated with increased health care utilization and costs. Regression models revealed that the factors most predictive of higher health care costs were child abuse, child neglect, and instability in out‐of‐home placements related to foster care. Other social determinants of health, such as parent risk factors, were not associated with health care costs. Child maltreatment and placement instability impacted health care costs primarily through large increases in behavioral health utilization and costs. Prevention and early interventions for children and families to decrease child maltreatment and increase foster care placement stability could reduce overall health care costs.