A multistage therapeutic community treatment system has been instituted in the Delaware correctional system, and its effectiveness has captured the attention of the National Institutes of Health, the Department of Justice, members of Congress, and the White House. Treatment occurs in a three-stage system, with each phase corresponding to the client's changing correctional status: incarceration, work release, and parole. In this study, 18-month follow-up data were analyzed for those who received treatment in a prison-based TC only, a work-release TC followed by aftercare, and the prison-based TC followed by the work release TC and aftercare. These groups were compared with a no-treatment group. Those who received treatment in the two-stage (work release and aftercare) and three-stage (prison, work release, and aftercare) models had significantly lower rates of drug relapse and criminal recidivism, even when adjusted for other risk factors. The results support the effectiveness of a multistage therapeutic community model for drug-involved offenders, as well as the importance of a work release transitional TC as a component of this model. 1 table, 5 figures, and 45 references