The aim of this research was to describe two fatal cases of Yersinia enterocolitica bioserotype 4/O:3 infection in non-human primates and to characterise the isolates by PCR and PFGE. In July 2004, two marmosets (Callitrix jacchuss) born in captivity in Zagreb Zoo, died following a few days of intermittent diarrhoea in intervals of 2 weeks. The pathomorphological diagnosis of the female (born in 1997) and the male (born in 1995) marmoset, was disseminated miliary necrosis of the liver. Y. enterocolitica 4/O:3 was isolated from both livers showing that monkeys are susceptible to this bioserotype. The ail gene, which is an essential chromosomal virulence factor in pathogenic Y. enterocolitica isolates, was present in the marmoset isolates. Two different PFGE patterns were obtained from the isolates of the male liver with NotI enzyme. One genotype of the male marmoset isolate was indistinguishable from the genotype of the female marmoset isolate when NotI, ApaI and XhoI enzymes were used indicating a common infection source for the marmosets. The genotypes of the marmoset isolates differed only slightly from one human (of seven Croatian isolates) and from one pig isolate (representing a common genotype found among human and porcine isolates in Germany) suggesting that raw pork fed to the marmoset could have been the infection source.