Indiana University-Purdue University Indianapolis (IUPUI) / Although approximately 60%-80% of detained adolescents have a psychiatric disorder, little is known about their utilization of mental health and substance-related treatment services upon release from detention. Given that treatment can potentially reduce symptomology and recidivism, the study examined detained adolescents’ post-detention treatment utilization and longitudinal patterns of use. Data were abstracted from the electronic juvenile justice records and medical records of 9664 detained adolescents (62.7% male; 34.8% White, 65.2% Black; 72.6% with disorder) with Medicaid coverage held in a Midwestern detention center at some time during 1998-2011. A series of statistical tests (e.g., chi-square, ANOVA, logistic regression, Kaplan-Meier survival analyses, Cox regression) were conducted to identify group differences in treatment utilization during the 14-year follow-up period. Following detention release, approximately 66.2% of adolescents were re-arrested and 54.9% were re-detained/incarcerated. Treatment utilization within two years post-detention was 36.7%; 31.4% obtained mental health treatment, 10.4% obtained substance-related treatment, 36.0% obtained outpatient treatment, and 6.2% obtained non-outpatient treatment. Among treatment users, 22.5% dropped out of treatment within 1-3 sessions and 40.6% experienced gaps (>45 days) between treatment services. Treatment utilization was significantly higher among males, White (vs. Black) adolescents, younger adolescents, violent (vs. non-violent) offenders, recidivists (vs. non-recidivists), and adolescents with mental disorders (vs. substance-related disorders). Variables associated with increased likelihood of post-detention treatment included: male gender, psychiatric disorder(s), pre-detention arrest(s), charge severity, violent offender, incarceration, and pre-detention treatment; age and Black race were associated with decreased likelihood of treatment. As one of the only longitudinal studies to examine treatment utilization among detained adolescents upon community reentry, findings suggest limited service utilization, as well as treatment gaps and disparities. Future research should focus on the treatment needs of detained adolescents, factors associated with disparities, and programs/policies to ensure consistent identification, referral, and connection to care for detained adolescents.