The objective of this study was to carry out a national survey to assess the Australian public's beliefs about causes and risk factors for mental disorders. A national household survey of 2,031 Australian adults was carried out. Half the respondents were presented with a vignette describing a person with major depression and the other half with a vignette describing schizophrenia. Respondents were asked to rate whether various factors are likely causes of problems such as that described in the vignette and to rate whether various groups are at higher or lower risk. For depression, social environmental factors were often seen as likely causes, which is consistent with the epidemiological evidence. However, genetic factors were considered as a likely cause by only half the population. For schizophrenia, social environmental factors were also often seen as causes, which is in contrast to the weak epidemiological evidence for such a role. Genetic factors attracted more support as a cause of schizophrenia than of depression. These findings point to areas where the mental health literacy of the population could be improved, particularly the over-emphasis on social environmental factors in schizophrenia. Of some concern was the belief of half the population that weakness of character is a likely cause of both depression and schizophrenia. This belief implies a negative evaluation of the sufferer as a person.