Yersiniosis, which is caused by pathogenic Yersinia enterocolitica or Yersinia pseudotuberculosis, poses a serious problem for zoological gardens engaged in breeding nonhuman primates. In Japan, Y. pseudotuberculosis in particular frequently causes fatal infection, and affected nonhuman primates may die unexpectedly or after a very short illness. Our epidemiological study in 17 zoological gardens in Japan suggested that Yersinia pseudotuberculosis-derived mitogen (YPM), which is a kind of super-antigenic toxin, might be the cause of, or at least the most important factor in, the high mortality of breeding nonhuman primates infected by Y. pseudotuberculosis in Japan. Furthermore, seroepidemiological study proved that pathogenic Yersinia is highly prevalent among breeding squirrel monkeys in Japan. It is likely that the monkeys that are pathogenic Yersinia positive have been inapparently or mildly infected by low pathogenic strains of Yersinia, not highly pathogenic strains of Yersinia, such as YPM-producing Y. pseudotuberculosis. In this review, we will describe the epidemiology of yersiniosis in breeding nonhuman primates in Japan.