The aim of the present study was to examine the treatment progress of both adolescent's and their families' functioning in a new compulsory residential treatment program. The sample consisted of 339 admitted adolescents (56.3% boys). The mean age at time of entry was 15.69 (SD=1.30). Adolescents stayed on average 9.42months (SD=4.66) in a new residential treatment program. Data on adolescents' internalizing and externalizing problems were assessed using self-reports, parent reports, and group care worker reports. In addition, adolescents reported their substance use and delinquency and parents also reported family functioning and level of perceived parental stress. The findings revealed a significant decrease in adolescents' self-reported internalizing and externalizing problems, delinquency, and substance use. According to parent ratings, a significant improvement was found concerning adolescents' problem behaviors during treatment. However, according care worker ratings, adolescents showed no improvement on internalizing problems and showed an increase in externalizing problems. Concerning families, although there was no improvement in family functioning, parental stress significantly improved over time. Further research should examine whether improvements experienced during treatment are maintained after treatment.