The concordance rate of Graves disease in pairs of identical twins of 30 to 60% points to the influence of environmental factors, and infections have often been incriminated in the pathogenesis9,12.17. More than 15 years ago we demonstrated an increased frequency of antibodies toYersinia enterocolitica(Y. ent.) serotype 31. which later was confirmed by others,19.20suggesting a link between infection withY. ent. and autoimmune thyroid diseases.