There is a dearth of research examining intervention effectiveness for ethnic minorities and few studies have investigated within-group differences in response to treatment. This study examined the prevalence of mental health problems among Anglo-and Mexican-American juveniles entering probation and their response to a comprehensive intervention designed to address drug, alcohol, and mental health in a culturally-sensitive manner. We hypothesized that all youths would demonstrate mental health improvements from pretest to posttest, and the improvements would be equal for Mexican-American youth of varying levels of acculturation and an Anglo comparison group. Participants included a total of 103 adolescents ages thirteen to eighteen years, of whom 59 percent were male and 81 percent were Mexican American. Hypotheses were supported, indicating this comprehensive, community-based intervention targeting delinquent adolescents and their families was effective in improving mental health regardless of ethnic background or level of acculturation. That is, regardless of group differences in mental health problems at intake, youth with different cultural orientations reported significantly reduced levels of internalizing and externalizing behavior problems at posttest.