Prairie voles are a monogamous species and males show paternal behavior. After mating, paternal responsiveness increases gradually during the gestation period, peaking before young are born. We examined the importance of cohabitation with a female and the time course for a gradual intensification of paternal care. Males housed with their brothers since weaning were separated. Each male was housed alone, with a strange female, or with a brother. A male housed with a female remained with her either until mating occurred or throughout gestation. Males in each group were tested for paternal behavior 3 times, in early, mid and late gestation periods. Males that were housed alone attacked the young more than those housed with another vole. A male exposed to a female, whether he had mated or not, engaged in more parenting than a male exposed to a brother. A male that remained with his mate during the gestation period was more parental than an isolated male that was housed alone. Contact with another vole reduces infanticidal tendencies; brief physical contact with a female, with or without mating, intensifies paternal responsiveness; and further cohabitation is not essential.