This case study presents a theoretical analysis of implementing mode deactivation therapy (MDT) (Apsche & Ward Bailey, 2003) family therapy with a 13 year old Caucasian male. MDT is a form of cognitive behavioral therapy (CBT) that combines the balance of dialectical behavior therapy (DBT) (Linehan, 1993), the importance of perception from functional analytic psychotherapy (FAP) (Kohlenberg & Tsai, 1993), and A.T. Beck's (1996) mode theory with a methodology to address the adolescents' belief system. MDT has been shown to be effective in a descriptive study with CBT (Apsche & Ward, 2002). The analysis of this case will illustrate the effectiveness of MDT as applied in family therapy. The individual in this case, David, was a troubled youngster. Although he denied ever experiencing physical and/or emotional abuse, his family of origin demonstrated extremely poor physical and emotional boundaries. David did report that he had been sexually victimized by a boy. He did not disclose the name of the boy because his parents were friends with the boy's family and the lack of appropriate boundaries in his family created an unstable atmosphere, causing David to feel compelled to follow his parent's wishes to refrain from disclosing the name. David was learning disabled. In order to make sense of and compensate for his unstable home life, David developed a complex system of personality disorder beliefs. Along with providing David with a way to cope with his unpredictable world, they also led him to commit numerous sexual offenses. David had previous unsuccessful treatment and basic cognitive therapy techniques were ineffective. Mode deactivation therapy was found to be more effective, due to its ability to address the personality disorder beliefs without challenging David to engage in dialectical debates. It was essential to incorporate David's family in his therapy since they were so involved in his life and treatment. Unexpectedly, his family made progress along with him, gaining insight into his beliefs as well as their own beliefs. David and his family learned how to balance their beliefs and modify their behavior. The family's progress inspired the application of MDT in family therapy. This theoretical case study represents mode deactivation therapy, applying theory to clinical practice within family therapy.