Using linked administrative data, we examine how child welfare system (CWS) contact affects adolescent behavioral health. We study youth ages 10–16 using a stacked difference-in-differences design comparing adolescents at referral to youth with later CWS contact. Behavioral health claims rise immediately and persistently after contact, especially following in-home services and foster care, with the largest increases for abuse-related referrals and PTSD. In contrast, suicidal ideation and behavioral-health emergency services do not increase, and instead decline, among foster care youth, suggesting the estimates reflect increased health care utilization rather than a decline in mental health.