A man, who had been treated for infantile hypertrophic pyloric stenosis (PS), was found to have 3 sons with the same condition. A genealogical table of his family showed that both his parents had relatives with PS. So far as it was known, none of his wife's relatives had the condition. It is suggested that the man's parents carried genes predisposing to PS and transmitted these to him in such quantity that he and all his children acquired the condition.