• The impact of community mental health centers on the utilization of psychiatric services in Monroe County, New York, was evaluated by means of data from the Monroe County Psychiatric Case Register. The catchment areas that received centers served as their own controls. In addition, yearly utilization rates were compared for areas that obtained centers with those remaining centerless. Utilization rates increased markedly in catchment areas with centers, while the percentage of patients seen at the Rochester Psychiatric Center decreased from all catchment areas. Community mental health centers increased the utilization rates of the poor, children, and young adults, while the treatment needs of patient subgroups such as alcoholics, drug addicts, and the elderly were last to be addressed. The data do not evaluate issues such as the character, quality, and effectiveness of care.