The authors sought to examine the association between adverse social determinants of health (SDoHs) and risk for self-harm among youths. The authors performed a retrospective longitudinal analysis of Ohio Medicaid claims data (April 1, 2016-December 31, 2018) of 244,958 youths (ages 10-17 years) with a primary psychiatric diagnosis. SDoHs were identified from ICD-10 codes and classified into 14 categories, encompassing abuse and neglect, child welfare placement, educational problems, financial problems, exposure to violence, housing instability, legal issues, disappearance or death of a family member, family disruption by separation or divorce, family alcohol or drug use, parent-child conflict, other family problems, social and environmental problems, and nonspecific psychosocial needs. Cox proportional hazards analysis was used to examine the association between SDoHs and self-harm (i.e., nonsuicidal self-injury or suicide attempt). Analyses controlled for demographic characteristics and comorbid psychiatric and general medical conditions. During follow-up after an index claim event, 51,796 youths (21.1%) had at least one adverse SDoH indicator, and 3,262 (1.3%) had at least one self-harm event. Abuse and neglect (hazard ratio [HR]=1.90, 99% CI=1.70-2.12), child welfare placement (HR=1.32, 99% CI=1.04-1.67), parent-child conflict (HR=1.52, 99% CI=1.23-1.87), other family problems (HR=1.25, 99% CI=1.01-1.54), and nonspecific psychosocial needs (HR=1.41, 99% CI=1.06-1.89) were associated with significantly increased hazard of self-harm. Adverse SDoHs were significantly associated with self-harm, even after controlling for demographic and clinical characteristics, underscoring the need for capturing SDoH information in medical records to identify youths at elevated suicide risk and to inform targeted interventions.