Hostility often co-occurs in parents and associates with increased aggression and inattention problems in children. In this population-based cohort of 484 mother–father–child neuroimaging trios, we investigated the degree to which associations of prenatal and childhood parental hostility would be associated with maternal, paternal, and child brain structural differences. Also, we examined whether hippocampal volumes of the parents or child mediate the association of prenatal parental hostility with child externalizing behaviors. Maternal and paternal hostility was assessed with the hostility subscale of the Brief Symptom Inventory at three time points: prenatally at 30 weeks’ gestation and when the child was 3 and 10 years old. During adolescence assessment wave (age 14), maternal, paternal, and offspring assessment included a magnetic resonance imaging. Child externalizing problems were assessed with Youth Self-Report Child Behavior Checklist. Our findings suggest that maternal and paternal hostility were each associated with smaller gray matter, white matter, and hippocampal volumes of their own and their partner's brain. Prenatal maternal but not paternal hostility was associated with smaller total gray matter, white matter, and hippocampal volumes in the offspring. The child's hippocampal volumes partially mediated the associations of prenatal parental hostility (latent construct) with adolescent externalizing behavior, even after adjusting for prior child externalizing problems. Moreover, parental psychopathology may have long-lasting neurodevelopmental correlates in children that underlie the intergenerational transmission of behavioral problems. The behavior of family members results from a system of interdependent dyadic relationships over time that associate with specific brain structural differences.