This study will rigorously and systematically evaluate an integrated service delivery approach using a design that reduces many of the methodological limitations in earlier work. Study participants will include opioid abusers with a current psychiatric disorder. All study participants will receive comprehensive drug abuse treatment that includes adequate daily doses of methadone. Study participants will be randomly assigned to either an onsite and fully Integrated Substance Abuse and Psychiatric Care condition (ISAP-Integrated) or an offsite and non-integrated Parallel Substance Abuse and Psychiatric Care condition (PSAP-Parallel). Patients assigned to the ISAP condition will receive all of their ambulatory psychiatric care in the ATS treatment program; those assigned to the PSAP condition will be referred for matched "doses" of psychiatric care to the Community Psychiatry Program, which is located on the same campus as the ATS program. All drug abuse treatment services will be provided in the ATS program. Patients will be evaluated for 12 months on a range of outcome measures, including psychiatric medication and therapy adherence, drug abuse treatment adherence, changes in psychiatric symptoms, including posttraumatic stress disorder (PTSD), drug use, exposure to traumatic events, psychosocial functioning, and retention in both psychiatric and drug abuse treatment.