This study compared the costs and outcomes associated with three treatment programs that served 149 individuals with dual disorders (i.e., individuals with co-occurring severe mental illness and substance use disorders) who were homeless at baseline. The three treatment programs were: Integrated Assertive Community Treatment (IACT), Assertive Community Treatment only (ACTO), and standard care (Control). Participants were randomly assigned to treatment and followed for a period of 24 months. Clients in the IACT and ACTO programs were more satisfied with their treatment program and reported more days in stable housing than clients in the Control condition. There were no significant differences between treatment groups on psychiatric symptoms and substance use. The average total costs associated with the IACT and Control conditions were significantly less than the average total costs for the ACTO condition.