The prevalence of HIV and other infectious diseases is high among offenders under community supervision. New York State has the largest number and percentage of prison inmates infected with HIV (5,500; 8.1%), and jails in New York City house more HIV-positive inmates than any other jail system in the country (Maruschak, 2004; Maruschak, 2001). Targeting those under criminal justice supervision with effective HIV/AIDS prevention and treatment services provides a valuable opportunity to prevent the spread of HIV and other infectious diseases and to improve the quality of life of infected persons. Although the need is clear, there is a paucity of research on and HIV/AIDS interventions for substance users or offenders with co-occurring mental illness disorders. Treatment Alternatives to Street Crime (TASC) is a court and community-based case management diversion program serving substance-abusing and co-occurring offenders. Evaluations of TASC indicate that it is effective at reducing substance use and recidivism among participants, yet few programs have added HIV/AIDS intervention components, or subjected those interventions to evaluation. The proposed project is a longitudinal, quasi-experimental research study of the effectiveness of an HIV/AIDS intervention that is being added to the TASC program in Brooklyn, New York, as well as an investigation into the factors that moderate the impact of the intervention and the correlates of HIV/AIDS risk behavior(s) and knowledge among offenders with drug abuse and co-occurring mental illness disorders who are being supervised in the community. The proposed study, which will produce many useful findings and products, builds on existing collaborations among RTI International, the proposed Principal Investigator, and the TASC programs in New York City.