A Solomon-four group experimental design was utilized in this study to assess the efficacy of cognitive group therapy with incarcerated psychopaths. The study involved two groups: the psychopath inmate group (n = 40) and the nonpsychopath inmate group (n = 40). The psychopath and nonpsychopath groups were delineated by utilizing the Psychopathy Checklist-Revised. These two groups of subjects were assigned to one of two conditions: either the treatment group or the nontreatment group. The experimental group participated in two 12-week criminal thinking groups (CTG) which focused on the 16 automatic criminal thinking errors put forth by Yochelson and Samenow (1976). Ten cognitive therapy techniques developed by Beck and Freeman (1990) were utilized by group leaders in this study. The Cognitive Style Questionnaire (CSQ) was utilized to measure changes in automatic criminal thinking errors with study participants. Selected scales on the CPI-R were also utilized as dependent measures in this study. Group therapy leaders also rated the frequency and effectiveness of cognitive therapy techniques utilized in each session. The results indicated that the psychopath's fragmentation and suggestibility criminal thinking errors decreased after participation in the CTG modules. The results also identified cognitive therapy techniques which may facilitate the psychopath's development of socially appropriate decision making and an increased awareness of their own criminal thinking patterns. This study was conducted at the California Men's Colony, a medium security prison in San Luis Obispo, California. (PsycINFO Database Record (c) 2016 APA, all rights reserved)