This study examined the impact of residential aftercare on recidivism following prison-based treatment for drug-involved offenders. A matched group quasi-experimental design. Survival regression analyses were used to predict time until rearrest. A logistic regression model was constructed for predicting aftercare completion. A 9-month in-prison therapeutic community (ITC) and several community-based transitional therapeutic communities (TTCs). Data were collected from 396 male inmates (293 treated, 103 untreated). Background information (gender, ethnicity, age, education level, criminal history and risk for recidivism) was abstracted from the state criminal justice databases and a structured interview led by clinical staff. During treatment process measures were based on inmate self-ratings of their counselors, program and peers. A post-treatment interview conducted by field research staff assessed satisfaction with transitional aftercare. Post-release recidivism was based on state-maintained computerized criminal history records. ITC treatment, especially when followed by residential aftercare, was effective for reducing post-release recidivism rates. Lower satisfaction with transitional aftercare treatment was associated with not completing the residential phase of community-based aftercare. Corrections-based treatment policy should emphasize a continuum of care model (from institution to community) with high quality programs and services.