The project was established to assess the effectiveness of prison-based drug treatment. The first established ITC facility was a 500-bed unit for males located in Kyle, Texas. Findings include the following: (1) Referrals to the Kyle ITC were made in accordance with legislative mandates; (2) Overall, ITC graduates reported favorable opinions about the program and counselors; (3) ITC graduates demonstrated marked reductions in their criminal and drug use activity from the 6 months before entering prison to the 6-month period before the 1-year follow-up interview after leaving prison; (4) ITC graduates were less likely to be rearrested after prison than were a matched comparison group of inmates from the general prison population who did not receive ITC treatment; and (5) ITC graduates who completed the first phase of aftercare -- 3 months at a residential Transitional Treatment Center -- had the most favorable outcomes. Notes, references, tables