OBJECTIVE: Results of randomized clinical trials of assertive community treatment for seriously mentally ill patients published between 1990 and 1994 are reviewed to synthesize the state of knowledge about this research and to clarify continuing research directions. METHODS: Randomized trials of interventions that used treatment principles and practices consistent with the Program for Assertive Community Treatment model or close adaptations whose results were published since 1990 were identified by literature searches using MEDLINE and PsychLit and by contact with investigators of ongoing trials. RESULTS: Controlled clinical trials have been conducted with a wide range of severely mentally ill populations, including patients in Great Britain, patients with recent-onset schizophrenia, veterans, dually diagnosed clients, and homeless persons. Methodological improvements in some studies include increased attention to monitoring the experimental and comparison interventions, as well as larger sample sizes and longer duration of the clinical trials than in earlier efficacy trials. Strong positive effects of assertive community treatment on hospital days and on patient and family satisfaction were found. Gains in functional outcomes, such as employment, may require interventions specifically targeted to these outcomes. CONCLUSIONS: Questions about the role of assertive community treatment as time-limited treatment, as an adjunct to other services and treatment, or as a comprehensive and continuous service system for adults with severe mental illness require further research. The growing research base should provide valuable information on costs, outcomes, and indications for assertive community treatment that can be evaluated by policy-makers.