This article describes the development of a 'key informant survey' to assess the performance of local systems of care for persons with a chronic mental illness. The measure yields ratings of: (1) the extent to which clients experience service delivery problems in 11 community support system elements, (2) overall performance of the community support system, and (3) the performance of local mental health authorities. Following pre-testing, the survey was administered to 699 respondents in nine U.S. cities. Internal consistency coefficients were found to be within acceptable ranges for all of the scales across all nine cities. Analyses comparing mean values for performance ratings showed that the nine sites could be arranged into three groups representing high, medium and low system performance. These findings support observations from site visits conducted over several years and suggest that the survey is a valid instrument for assessing local systems of care.