Background The proportion of people with mental disorders in treatment is relatively small in low and middle income countries. However, little is known about patterns of recent service use in a country like South Africa. Methods A nationally representative household survey of 4,351 adult South Africans was carried out. Twelve-month DSM-IV disorders were determined using the WHO composite international diagnostic interview (CIDI). Prevalence and correlates of treatment were assessed among respondents with anxiety, mood and substance use disorders. Results One-fourth (25.5%) of respondents with a 12-month disorder had received treatment in the past 12 months either from a psychiatrist (3.8%), nonpsychiatrist mental health specialist (2.9%), general medical provider (16.6%), human services provider (6.6%), or complementary-alternative medical (CAM) provider (5.9%). Only 27.6% of severe cases had received any treatment. In addition, 13.4% of respondents with no disorder had accessed services in the past year. Blacks were significantly more likely than other racial groups to access the CAM sector while Whites were more likely to have seen a psychiatrist. Conclusions The majority of South Africans with a 12-month mental disorder have unmet treatment needs. In addition to a greater allocation of resources to mental health services, more community outreach and awareness initiatives are needed.