The Walden House Comprehensive Assessment and Treatment Services (WH-CATS) Project will provide mental health services to substance abusers with HIV/AIDS at Walden House, Inc., in San Francisco, California. Treatment will include comprehensive psychiatric assessments and evaluation, psychiatric services, and mental health and counseling services. Pre- and post-test counseling also will be offered. The agency anticipates serving over 500 unduplicated individuals with an HIV/AIDS and substance abuse diagnosis each year; an additional 350 unduplicated clients will receive pre- and post-test counseling. The target population is the HIV/AIDS substance abuser. The WH-CATS project will treat a wide range of clients; a majority will be people of color, and services will be both gender and ethnic-specific. The primary goal of the project is to improve the quality of life of HIV/AIDS substance abusers. A manual, updated annually, will document both the services and the evaluation of the project.