Yersinia bacteria, as an etiologic factor of yersiniosis, commonly occur in nature in all climatic zones. These bacteria were isolated form soil, drinking water, surface waters, sewage, fodder and food, and penetrate into the environment with the faeces of infected animals, ill or asymptomatic carriers. Animals are the reservoir, and frequently, similar to the environment, they constitute the source of infection in humans, most often by the alimentary route. Yersiniosis is an acute or chronic contagious zoonosis of various clinical image. The infection is most often manifested by the symptoms of alimentary poisoning of various intensity, sometimes false appendicitis, and sometimes there occurs a non-intestinal location of the disease. In severe forms, relapses and complications of the disease are observed. The clinical and laboratory diagnostics of yersiniosis is dificult. A precise determination of the etiologic factor, especially in the disease with a severe course, is of great importance, because Yersinia bacteria may differ by sensitivity to antibiotics according to their species and serotype.