Why does the burden of mental disorders persist in established market economies? There are four possibilities: the burden estimates are wrong; there are no effective treatments; people do not receive treatment; or people do not receive effective treatments. Data from the Australian National Survey of Mental Health and Wellbeing about the two commonest mental disorders, generalized anxiety disorder and depression, have been used in examining these issues. The burden of mental disorders in Australia is third in importance after heart disease and cancer, and anxiety and depressive disorders account for more than half of that burden. The efficacy of treatments for both disorders has been established. However, of those surveyed, 40% with current disorders did not seek treatment in the previous year and only 45% were offered a treatment that could have been beneficial. Treatment was not predictive of disorders that remitted during the year. The burden therefore persists for two reasons: too many people do not seek treatment and, when they do, efficacious treatments are not always used effectively.