Yersiniosis is an acute infectious disease, which course may differ in dependence to age at which patient was infected. It may cause reactive arthritis in adults and seldom in children. The aim of the study was evaluation of anti Yersinia enterocolitica antibodies titer in group of patients with previously diagnosed Lyme disease. The subject of the study was group of 76 males, foresters from north-eastern Poland at the age of 26 to 60 years (x = 41), with long term history of Lyme disease. In 10% of examined patients positive anti Yersinia enterocolitica antibodies titer was observed.