In mice, parthenogenetic embryos die at the early postimplantation stage as a result of developmental requirements for paternally imprinted genes, particularly for formation of extraembryonic tissues. Chimaeric parthenogenetic<==>normal mice are viable, however, due to non-random differences in distribution of their two cell types. Species differences in imprinting patterns in embryo and extra-embryonic tissues mean that there are uncertainties in extrapolating these experimental studies to humans. Here, however, we demonstrate that parthenogenetic chimaerism can indeed result in viable human offspring, and suggest possible mechanisms of origin for this presumably rare event.