The objective of this study was to assess the efficacy of the Ross Programme for adolescent boys within residential care, which was developed to tackle antisocial behaviour and is based on a cognitive behavioural model. The main aim of the programme is to teach participants skills and values that are required for prosocial competence and that are antagonistic to antisocial behaviour. The study was designed to compare, on a variety of measures, a group of adolescents who completed the Ross Programme with a group who had not yet started the programme. Significant effects of the programme on level of risk of general re-offending, problem-solving ability, behaviour, and criminal attitudes were observed for the treatment group. In comparison, the control group showed no significant improvements in any of the treatment outcome measures.