This research study compared the efficacy of three treatment methodologies for adolescent males in residential treatment with conduct disorders and/or personality dysfunctions and documented problems with physical and sexual aggression. The results showed that Mode Deactivation Therapy, an advanced form of cognitive behavioral therapy based on Beck's theory of modes, was superior to traditional Cognitive Behavioral Therapy and Social Skills Therapy in reducing both physical and sexual aggression. At the same time, Mode Deactivation Therapy was the only treatment of the three that significantly reduced sexual aggression for these youth. (Contains 6 tables.)