The study is focused on two research questions: What are the public's estimates of the prevalence of depression, schizophrenia, bulimia nervosa and anorexia nervosa? What is the relationship between the estimated prevalence of the mental disorders and the public's desire for social distance? Analyses are based on a telephone survey in two large German cities (Hamburg and Munich, N=2014, response rate 51%). Vignettes with typical signs and symptoms suggestive of a depression, schizophrenia, bulimia nervosa and anorexia nervosa were presented. Respondents were asked about the lifetime prevalence of the mental disorders and their desire for social distance. Across all four disorders under study the respondents markedly overestimate the rates of lifetime prevalence. Increasing prevalence estimation is associated with a significant decrease in the desire for social distance in case of schizophrenia. As for depression, anorexia nervosa and bulimia nervosa there are no significant associations. Many campaigns aimed at reducing stigma emphasize the high prevalence of mental disorders. The assumption of these campaigns is that reduction of the perceived distinction leads to a decrease of the desire for social distance towards those afflicted. Our results indicate that this may not generally be an effective way to reduce stigma.