Only in the last few years has Yersinia enterocolitica been recognized as an etiologic agent. The organism, however, is widespread in both the animate and inanimate environments. It has been isolated and recovered from a variety of sources including fecal material, foodstuffs, and water, but vehicles of disease transmission are not fully delineated or understood. The bacteriology of Y. enterocolitica is reviewed and recommended laboratory methodology is described.