The prevalence of Addison's disease (chronic adrenal failure) has not been widely investigated and is usually given as 39 in a million. We conducted a prevalence study using a postal survey of general practitioners in Coventry. Three quarters (139/188) replied, representing 79/85 (93%) of the practices. Thirty cases of Addision's disease were found from a total patient list of 323852, of which a third were tuberculous in origin and two-thirds non-tuberculous (12/30 autoimmune, 8/30 unclassified).