The proposed project is a five-year program consisting of a controlled clinical trial, studying 220 patients with HCV infection enrolled in methadone maintenance treatment (MMT). The HCV Medical Care Study is a randomized trial to test the efficacy of On-site HCV Medical Care provided at the MMT program versus Off-site care at the Gastroenterology (GI) Clinic. HCV antibody positive MMT patients (N=220) will be randomly assigned to receive HCV medical services either through an integrated delivery model located on-site in the MMT clinic, or through usual off-site referral to the GI Clinic. The main outcomes will be the rates of attaining SVR and completion of HCV treatment, as well as other measures of HCV-related health outcomes and quality of life. Participants will be evaluated for Axis I psychiatric diagnoses and will complete psychiatric measures at monthly intervals throughout the study. Psychiatric diagnosis will be made using the Structured Psychiatric Interview for the DSM-IV (SCID) and psychiatric symptom severity will be assessed for depression, mania, anxiety, and psychosis. Drug use measures, and quality of life measures will also be obtained. These data are expected to yield new knowledge about the efficacy of providing on-site HVC medical care in substance abuse treatment programs. They will provide a comparison of psychiatric diagnoses and psychiatric symptom presentation in HCV positive IDUs who choose to receive HCV treatment and those who do not choose to follow through with HCV treatment and will describe changes in psychiatric symptoms before, during, and after HCV medical care. Finally, the studies will also provide information about the influence of psychiatric symptoms and drug and alcohol use on HCV medical outcomes such as treatment completion and SVR.