One of the major problems in measuring community mental health status is the lack of consensus among mental health workers in psychiatry, psychology, sociology, and epidemiology as to what constitutes mental illness. Additionally, changing social mores preclude a definition of mental illness in behavioral terms. An operational definition of mental illness is proposed that bypasses these difficulties and makes it possible to use data already available as indicators of community mental health problems. This definition uses only the "tangible" evidence of mental illness, i.e., suicides and people institutionalized or receiving ambulatory care for conditions other than physical illness. These statistics are then transformed into indices of community mental illness that are the basis of estimates of mental illness costs. Five states in the United States are compared with respect to mental health status and mental illness costs. Limitations of the indices and cost estimates are discussed. (Author)