Background: Previous studies have found that the reliability of the lifetime prevalence of bulimia nervosa is low to moderate. However, the reasons for poor reliability remain unknown. Aims: We investigated the ability of a range of variables to predict reliability, sensitivity, and specificity of reporting of both bulimia nervosa and major depression. Method: Two interviews, approximately 5 years apart, were completed with 2163 women from the Virginia Twin Registry. Results: After accounting for different base rates, bulimia nervosa was shown to be as reliably reported as major depression. Consistent with previous studies of major depression, improved reliability of bulimia nervosa reporting is associated with more severe bulimic symptomatology. Conclusions: Frequent binge eating and the presence of salient behavioural markers such as vomiting and laxative misuse are associated with more reliable reporting of bulimia nervosa. In the absence of the use of fuller forms of assessment, brief interviews should utilise more than one prompt question, thus increasing the probability that memory of past disorders will be more successfully activated and accessed. Declaration of interest: None.