Background: Although adolescents are often referred to residential treatment centres because of severe externalizing behaviours, a vast majority demonstrated comorbid symptoms of depression and anxiety. Covert internalizing symptoms in these adolescents might be easily unrecognized and therefore untreated. Adolescents with mild intellectual disability (MID) are overrepresented among youth with both externalizing and internalizing problems. There are yet few treatment programs available for adolescents with both externalizing and internalizing problems. Methods/design: The CBT-based resiliency program, Op Volle Kracht (OVK), which is based on the US Penn Resiliency Program (PRP), was adapted to suit the needs of adolescents with both externalizing and internalizing problems, either with or without MID, in Dutch residential treatment centres. The effectiveness of this group intervention program of eight sessions will be tested in a randomised controlled trial (RCT) with N = 182 adolescents aged 12-16, allocated to either the target intervention plus treatment as usual (OVK + TAU) or treatment as usual only (TAU). The main outcome variables include depressive symptoms (primary), anxiety, behavioural problems, and group therapeutic climate. Cognitive styles and coping styles will be included as possible mediators. Assessments take place at baseline (T1), one week before the start of the program (T2), immediately after the program (T3), and at three months follow-up (T4). Discussion: The program assets include its wide implementation possibilities due to low costs, the short duration of the program and the delivery by group care workers, and its suitability for adolescents with MID. Further strengths of the present study design include its robust method (RCT), the ecological validity, and the inclusion of possible mediators of treatment effect. The program emphasizes individual risk factors for depression rather than social and family factors. Implications for practice and future research are discussed.