Differences between white and ethnic client psychosocial functioning, psychiatric and substance abuse symptomatology, and service utilization costs from a longitudinal clinical trial examining the relative cost effectiveness of three specialized interventions for dual disorders are compared within the study sample and to the existing literature. Ethnic clients comprised 30% of the treated sample, had lower psychosocial functioning scores (rated and self-reported), and received less supportive treatment services during the first 6 months of the intervention program; however, their overall outcomes were equivalent to those of white clients at 6 months. There were no functioning or symptom outcome differences across the three treatment groups, but the 12-step group had the highest intensive and supportive service costs over time, and also the greatest reductions in intensive service costs after 6 months. Clinical issues are described and the clinical implications for more effectively serving dually diagnosed ethnic clients are outlined.