Although research has repeatedly shown that residential care for youth with a serious behavior problem has little rehabilitation success, there is a group of youth for whom residential care in a locked setting is necessary. In this article, a manualized therapeutic residential treatment model for adolescents with serious behavior problems, MultifunC, is evaluated. The program theory of MultifunC is based on a review of the literature and synthesis effective treatment components. This study included 80 youth aged 15–17 years with a medium high or high risk for reoffending. Half of the participants received MultifunC, and half treatment as usual (TAU). Although non-randomized, the two groups were found to be equivalent on important background variables. After 24 months, this first evaluation of MultifunC demonstrated that youth participating in MultifunC had a reduced need for residential care in a locked setting as well as out-of-home placement in general compared to youth in the TAU group. The economic analysis found MultifunC to be a cost-effective alternative to TAU due to the reduced need of residential care in locked settings. There were no significant effects on reoffending or psychiatric care.