The impact of intensive outpatient mental health interventions (in a dual diagnosis clinic) on the hospitalization rate and length of stay was examined for 28 adults with mental retardation and severe psychiatric disorder. They were selected on the basis of frequent use of mental, medical, and social services. Charts were reviewed for the 12-month periods before and after referral to the program to compare service utilization. A single group pretest-posttest design with no control group was employed. Correlated t tests comparing the pre- and postprogram number of hospitalizations and lengths of stay indicated significant decreases in both hospitalizations and lengths of stay after program entry, which may result in significant reductions in hospital costs.