Treatment for adolescent problem behavior has been given extensive attention in the literature due to the serious nature of the problem and the potential risk to others and the community. As the needs of an increasingly diverse juvenile population intensify and mounting evidence suggests ethnic minority youth receive disparate treatment across juvenile justice decision points, juvenile justice and mental health personnel are equally concerned with identifying effective interventions which work across ethnic and cultural groups. However, very few rigorous research studies have been conducted to empirically evaluate the effectiveness of evidence-based interventions with ethnic minority populations. In 2001, Functional Family Therapy (FFT) was implemented in Miami, Florida to provide an evidence-based family intervention for the treatment of adolescent offenders involved with the juvenile justice system. The current study is an evaluation of the Miami FFT program and is the first of its kind to investigate the effectiveness of FFT across client ethnic groups. In a diverse sample of juvenile offenders, FFT was compared to non-family juvenile offender treatment (NFT) and within-group comparisons were made on a number of outcomes including recidivism, crime severity, program completion, and individual symptomatology across client ethnic groups. A significant difference was noted between the groups in pre-treatment crime severity scores with the FFT group evidencing significantly higher pre-treatment crime severity compared to the NFT group. After controlling for the effect of these pre-treatment differences, results indicated FFT is as effective as non-family juvenile offender treatment (NFT) in reducing recidivism and crime severity, but with more severe offending youth. Within-group analyses revealed FFT was equally effective across diverse client ethnic groups in terms of recidivism, post-treatment crime severity, and program completion rates. Finally, results indicated that therapist rated adherence to the FFT model was only moderately related to treatment outcomes. While additional research will be necessary to establish FFT as an effective evidence-based intervention for juvenile offenders across diverse client ethnic groups, the present evidence suggests that FFT can be successfully applied to ethnic minority groups and is a promising treatment for this population.