Brain, oxytocin, and parenting behavior were measured in primary-caregiving mothers, secondary-caregiving fathers, and primary-caregiving homosexual fathers raising infants without maternal involvement. Parenting integrated functioning of two neural networks: subcortical-paralimbic structures implicated in emotional processing and cortical circuits involved in social understanding. Mothers showed greater activation in the emotional processing network and fathers in the socio-cognitive circuits, which were differentially linked with oxytocin and behavior.