The Amity TC is located at R. J. Donovan medium-security Correctional Facility in San Diego. The program used a three- phase treatment process that has been described in the literature. The initial phase (2 to 3 months) included orientation, clinical assessment of resident needs and problem areas, and planning interventions and treatment goals. During the second phase of treatment (5 to 6 months), residents were provided opportunities to earn positions of increased responsibility by showing greater involvement in the program and through intense emotional work. Encounter groups and counseling sessions focused on self-discipline, self-worth, self-awareness, respect for authority, and acceptance of guidance for problem areas. During the re-entry phase (1 to 3 months), residents strengthened their planning and decision-making skills and worked with program and parole staff to prepare for their return to the community. For the evaluation, data collection consisted of face- to-face interviews and reviews of criminal justice records for a sample of 715 male inmates. Subjects were randomly assigned to the prison TC intent-to-treat group and no-treatment control group from a waiting list of inmates who had volunteered for substance abuse treatment in the Amity program. Reductions in reincarceration rates of more than 40 percent at 12 months and more than 50 percent at 24 months after release from prison were found for the group that completed prison TC plus aftercare. These improvements remained significant after controlling for client characteristics that have been identified as predictors of recidivism. The findings support the efficacy of prison TC plus aftercare in reducing reincarceration rates among inmates treated for substance abuse. 3 tables, 2 figures, and 20 references