The process portion of the evaluation found that the target population for the program is being served, as those admitted to the program have extensive criminal and substance abuse histories, as well as substantial unmet needs for treatment, vocational, and educational programming. Thanks to the strong support received from the Illinois Department of Corrections, the program has developed so as to ensure its clinical integrity and the availability of sufficient resources for needed services. A consistently low rate of inmates has been removed from the program for disciplinary reasons, despite the serious criminal histories of the population. During the course of program participation, inmates improved their levels of psychological and social functioning, as well as their criminal thinking patterns. Significant improvements have been made to the postrelease phase of the program over the 6 1/2 years of program operation. As a result of the in-prison treatment services and aftercare received, those inmates released from Sheridan had a 16-percent lower likelihood of being returned to prison after 3 years in the community compared to a statistically similar control group of inmates released from other Illinois prisons during the same time period. The largest reductions in recidivism, both in terms of rearrest and return to prison, were found among Sheridan releasees who successfully completed aftercare. Since the rates of aftercare treatment completion have improved substantially over the past year, it is likely that reductions in recidivism among Sheridan releasees will be even larger. 27 figures, 18 tables, and 31 references