This article provides a brief overview of the prevalence, risk factors and characteristics of persons with mental or behavioural problems in Australia. Unless otherwise stated, this article presents information sourced from the 2004-05 ABS National Health Survey (NHS). It should be noted that the 2004-05 NHS excluded persons in hospitals, nursing and convalescent homes and hospices and hence the data relates only to persons in private dwellings. This article also draws on data from the 2003 Survey of Disability, Ageing and Carers (SDAC) and other ABS and non-ABS sources. Mental or behavioural problems were identified in the 2004-05 NHS through the self-reported information on long-term conditions obtained by the survey