Background: The National Mental Health Services Survey (N-MHSS), conducted by the Substance Abuse and Mental Health Services Administration (SAMHSA), is an annual survey of all known public and private mental health treatment facilities in the United States. The survey is the only source of national and state-level data on the mental health services reported by both publicly and privately operated specialty mental health care facilities. Method: The National Mental Health Services Survey (N-MHSS) is a biennial survey designed to collect information from all facilities in the United States, both public and private, that provide mental health treatment. N-MHSS provides the mechanism for quantifying the dynamic character and composition of the United States mental health treatment delivery system. Results: The 2010 N-MHSS instrument collected information on specific facility characteristics and the number of clients in treatment on the survey reference date. It included questions on topics such as facility type, operation, primary treatment focus, management characteristics, client demographics, supportive services, mental health treatment approaches, special programs or groups, types of payment/funding accepted, languages in which treatment is provided, and a one-day client/patient census by type of service setting. Conclusion: The N-MHSS data can be used to describe the nature and scope of mental health services provided in state-funded, state-operated, and other (e.g., private for-profit, and nonprofit) mental health treatment facilities. The N-MHSS data can also be used to conduct comparative analyses and forecast future resource needs. Additionally, the N-MHSS data are used to update SAMHSA's Inventory of Behavioral Health Services, an inventory of all known mental health and substance abuse treatment facilities in the United States, and to update the information in the mental health component of SAMHSA's online Behavioral Health Treatment Services Locator (