Paternity likelihood was tested in a population of splendid fairy-wrens Malurus splendens by allozyme electrophoresis. A total of 91 offspring of 24 dams and 37 putative sires were typed at 10 polymorphic loci. All young were compatible with their dams but at least 65% were not fathered by any of the males in their group. A long-term study of this wren population has shown that the males are sedentary, show little evidence of dispersal and help care for the nestlings and fledglings in their group. Had the senior male sired all the offspring in his group, there would have been a high incidence of close inbreeding. The promiscuous mating system demonstrated here would reduce the level of inbreeding in the population but still allow individuals the security of group-living in a stable year-round territory.