Abstract. Here we provide evidence of multiple paternities in naturally mated sows under conditions ensuring that (a) sows had the same probability of being mated by any of the available boars and (b) no differences in hybrid vigour existed. Total DNA was obtained from 19 Gochu Asturcelta piglets from three different sows, each with the same chance of natural mating with two different boars. A set of 20 microsatellites were typed on all the individuals. The program CERVUS was used to asses the informative ability of the microsatellite set and to perform paternity assignment. Allelic frequencies at population level were obtained using a total of 141 Gochu Asturcelta individuals. Offspring were always assigned to a candidate boar with high statistical confidence. All litters had different parents. Our results show that multiple paternities are possible in domestic pigs under natural mating. Furthermore, the current study can be useful to further understand the mating system of the wild boar.