The purpose of this project is to conduct a systematic program evaluation of the Stonewall Project, which is currently deployed in four community settings by the San Francisco AIDS Foundation. The Stonewall Project is an innovative, outpatient substance abuse treatment program for methamphetamine-using MSM that is implementing evidence-based interventions (i.e., the Matrix Model) in a real world clinical setting. In collaboration with the Stonewall Project, we will conduct a comprehensive treatment outcome evaluation with 150 participants who are newly initiating services. Participants in the treatment outcome evaluation will complete quantitative assessments at baseline as well as three and six months follow-up to examine changes in substance use and HIV risk-taking behavior. We will also build the capacity of the Stonewall Project to conduct ongoing evaluation efforts by developing a web-based assessment system. This system will automate existing self-monitoring activities that participants complete prior to each counseling session at the Stonewall Project to facilitate ongoing evaluation of treatment outcomes.