Yersinia enter ocolitica bacteria are facultatively anaerobic gram negative rods belonging to the family of Enterobacteriaceae. 1 They are medically important organisms, since they can cause a wide variety of infections which are sometimes fatal. The most common clinical forms are acute enteritis (in young children and infants) and appendicitis-like syndrome (in older children). Less frequently and primarily in adults, extra-intestinal inflammations as arthritis and erythema nodosum can be associated with Y. enter ocolitica infections. Finally, Y. enterocolitica disseminated by blood may cause rare infections in different organ systems. 2 Y. enterocolitica infections often mimick other diseases, leading to incorrect diagnosis and unnecessary laparotomy in the case of appendicitis-like syndrome. Good diagnostic tools are therefore important.