CONTEXT: Frequently, during grand rounds and other medical conferences, bold statements are made regarding 'exotic medical facts'. Such exotic expert opinions are frequently voiced with great conviction and are usually subsequently assimilated by junior staff as medical fact. METHODS: The level of scientific evidence for each exotic expert opinion expressed during daily grand rounds over a 4-month period was evaluated. If, following a short discussion of the statement, any doubt as to the merits of the claim persisted, the person who made the statement was asked to perform a search in the medical literature on the subject. RESULTS: In total, 25 cases of exotic expert opinion were identified during the study period. Of these, 22 statements were made by senior staff and 3 by residents. Careful review of the literature showed only 8 of the statements were actually evidence-based. In 17 cases the available literature actually contradicted the statement (n = 13) or no literature on the subject could be located (n = 4). Although opinions were most often expressed by staff members, the reviews of their merits were more often performed by residents. CONCLUSIONS: The vast majority of exotic expert opinions expressed by senior staff members during grand rounds are not evidence-based. Thus, great care must be taken to ensure that exotic expert opinion is not accepted as factual without careful review. Furthermore, this study shows that although seniority is (as expected) associated with a higher incidence of voicing exotic expert opinion, it is negatively associated with reviewing the merits of such opinion. © 2007 Blackwell Publishing Ltd.