Meta-analysis of 58 controlled studies and analysis of the claims files for the Blue Cross and Blue Shield Federal Employees Plan for 1974-1978 provide mutually supporting evidence of the cost-offset effects of outpatient mental health treatment. These two complementary resources provide a powerful tool for investigating the nature of associations between mental health services and subsequent reductions in the use of other medical services. The authors found that the reductions in use of medical services are associated with inpatient rather than with outpatient utilization and tend to be larger for persons over 55 years of age.