Our study examined co-occurring substance use and major depressive disorders among justice-involved adolescents to inform behavioral health services planning within U.S. criminal justice systems. We used data from the 2015-2017 administrations of the National Survey on Drug Use and Health (NSDUH), an annual survey of non-institutionalized U.S. individuals aged 12 and older, to yield a national sample of 41,579 adolescents. Rates of co-occurring disorders were 4.5 times higher among justice-involved adolescents than non-justice-involved adolescents, with 6.3% of justice-involved adolescents meeting criteria for co-occurring disorders in the past year compared to 1.2% of non-justice-involved adolescents. Justice involvement was associated with greater substance use treatment but not mental health treatment. High rates of co-occurring disorders among justice-involved adolescents suggest the criminal justice system to be a unique opportunity for treatment engagement. The integrated mental health and substance use treatment needs of justice-involved adolescents with co-occurring disorders should be prioritized.