Participants were 39 inpatients of the Forensic Psychiatric Center Veldzicht. All of the patients had committed serious crimes. The goal of the multidisciplinary treatment was to reduce the risk of reoffending by improving coping and social skills; reducing distrust, hostility, anger, and aggression; improving social awareness and self-confidence; and improving well-being. Treatment was based on cognitive-behavioral principles. A support milieu was created in the ward while behavior treatment principles were integrated in the ward's functioning. Staff members were all trained in cognitive behavioral treatment principles, with the focus on behavior modification through reinforcement, shaping, modeling, and providing "time out." Most patients had a daily program that consisted of occupational therapy and education in addition to treatment therapies tailored to particular needs. Scores on a battery of psychological and behavioral tests were conducted at baseline and at multiple times over a period of 12 to 18 months. The clinical significance index was assessed only for the last follow-up assessment. To be clinically significantly improved according to this index, patient scores had to be reliably changed and closer to the mean score of a normal population. As a group, the patients showed significant improvements over time on psychopathological symptoms, personality traits, and coping. A significant decrease in oppositional behaviors was reported by the staff; however, only a minority of patients showed reliable change over time at the individual level. The significance of these findings for treatment strategies are discussed. 4 tables and 36 references