This article summarizes results from four research studies (n = 902) that examined the effectiveness of the modified therapeutic community (MTC) for clients with co-occurring disorders (most with severe mental disorders). Significantly better outcomes for MTC were found across four experimental versus control comparisons on 23.1% (12 of 52) of primary outcome measures of substance use, mental health, crime, HIV risk, employment, and housing. Study limitations included the potential for selection bias, limited measurement of program fidelity, and insufficient examination of the relationship between treatment dose and outcome. Future research should emphasize clinical trial replications, multiple outcome domains, and further development of continuing care models. Given the need for research-based approaches, the MTC warrants consideration when program and policy planners are designing programs for co-occurring disorders.