Treatment outcomes 1 year after release from prison were compared for two subgroups of male inmates with co-occurring serious mental illness and chemical abuse (MICA) disorders, those with a diagnosis for Antisocial Personality Disorder (APD), and those without a diagnosis of APD. The foundation study had randomly assigned inmates to either Modified Therapeutic Community (MTC) or Mental Health (MH) treatment programs. Results presented in this paper support earlier findings of the overall effectiveness of MTC treatment in correctional settings, and extend these findings to encompass the subgroup of offenders whose co-occurring disorders include APD. An intent-to-treat analysis (all study entrants) and a matched group analysis (Medium propensity stratum) found significantly greater improvement on measures of criminal activity and substance use for those in the MTC group (as compared with the MH group) regardless of APD diagnosis, and showed that negative treatment effects were not linked to APD. Differences between the treatment groups were consistent and significant, and persisted after an examination of various threats to validity (e.g., initial motivation, exposure to treatment, severity of substance use, severity of APD symptomatology). These findings are encouraging and consonant with other studies of the effectiveness of TC approaches for APD populations receiving substance abuse treatment in correctional settings. Given the available evidence and the demand for effective programming for offenders with co-occurring disorders, criminal justice program and policy makers should strongly consider developing modified TC programs across a full array of mental disorders, including APD. (Contains 4 tables and 3 notes.)