The National Institute of Mental Health Epidemiologic Catchment Area Survey is a comprehensive, community-based survey of mental disorders and use of services by adults, ages 18 and older. Diagnoses are based on the criteria in the "Diagnostic and Statistical Manual of Mental Disorders," third edition, and were obtained in five communities in the United States through lay-interviewer administration of the National Institute of Mental Health Diagnostic Interview Schedule. Results from the survey provide the public health field with data on the prevalence and incidence of specific mental disorders in the community, unbiased by the treatment status of the sample. The population with disorders is estimated, and the survey findings that respond to some of the most common requests for information about the epidemiology of mental disorders in the United States are highlighted briefly. Based on the survey, it is estimated that one of every five persons in the United States suffers from a mental disorder in any 6-month period, and that one of every three persons suffers a disorder in his or her lifetime. Fewer than 20 percent of those with a recent mental disorder seek help for their problem, according to the survey. High rates of comorbid substance abuse and mental disorders were found, particularly among those who had sought treatment for their disorders.