ABSTRACT BackgroundSouth Africa's history and current social conditions suggest that mental disorders are likely to be a major contributor to disease burden, but there has been no national study using standardized assessment tools.MethodThe South African Stress and Health Study was a nationally representative in-person psychiatric epidemiological survey of 4351 adults (aged 18 years) that was conducted as part of the WHO World Mental Health (WMH) Survey Initiative between January 2002 and June 2004. Twelve-month prevalence and severity of DSM-IV disorders, treatment, and sociodemographic correlates were assessed with Version 3.0 of the WHO Composite International Diagnostic Interview (CIDI 3.0).ResultsThe 12-month prevalence of any DSM-IV/CIDI disorder was 16.5%, with 26.2% of respondents with disorder classified as severe cases and an additional 31.1% as moderately severe cases. The most common disorders were agoraphobia (4.8%), major depressive disorder (4.9%) and alcohol abuse or dependence (4.5%). Twenty-eight percent of adults with a severe or moderately severe disorder received treatment compared to 24.4% of mild cases. Some 13.8% of persons with no disorder received treatment. Treatment was mostly provided by the general medical sector with few people receiving treatment from mental health providers.ConclusionsPsychiatric disorders are much higher in South Africa than in Nigeria and there is a high level of unmet need among persons with severe and moderately severe disorders.