As incarceration levels continue to soar, increased attention has been paid to the link between criminal behavior and drug use and how to effectively address drug abuse within the criminal justice system. In an effort to contribute to this literature, the current study provides a long-term economic analysis on the treatment of criminal offenders by estimating the costs associated with in-prison and community-based treatment and comparing them to the number of days reincarcerated over a 5-year, post-release follow-up period. Data were drawn from 4 groups: in-prison treatment only (N=236), in-prison and after-care treatment (N=105), all after-care participants (N=341), and a control group receiving no treatment (N=235). Results indicated that those in the in-prison and after-care treatment group had 291 fewer reincarceration days during the 5-year study period. The relative cost associated with both in-prison and after-care treatment was $11,969 per offender and yielded a cost per avoided incarceration day of $41 relative to the in-prison only treatment group. The in-prison only treatment group was not cost effective due to the higher treatment cost and the greater number of days spent reincarcerated. Thus, the analysis reveals that the role of aftercare is pivotal in determining the cost-effectiveness of drug offender treatment models. The in-prison treatment program was determined to be cost-effective only when combined with the after-care treatment, producing a higher overall treatment cost but a lower reincarceration cost. Future research should focus on bringing health economists into the evaluation of criminal justice substance abuse treatment to create a multidisciplinary research base. Tables, references