In Europe and North America, Yersinia enterocolitica has been reported with increasing frequency in recent years as a cause of diarrhea, mesenteric adenitis, terminal ileitis, and other clinical syndromes. Yersiniosis, with its protean manifestations, may occur as an endemic disease or in epidemics in communities, families, schools, or hospitals. The clinical and epidemiologic features of this disease are reviewed, as are aspects of its pathogenesis, diagnosis, treatment, and prevention.