This study used a prospective adoption design to investigate effects of prenatal and postnatal parent depressive symptom exposure on child hypothalamic-pituitary-adrenal (HPA) activity and associated internalizing symptoms. Birth mother prenatal symptoms and adoptive mother/father postnatal (9-month, 27-month) symptoms were assessed with the Beck Depression Inventory in a sample of 192 families as part of the Early Growth and Development adoption Study. Child morning/evening cortisol levels and child symptoms of internalizing disorders (according to mother/father report on the Child Behavior Checklist) were assessed at 54 months, and birth mother diurnal cortisol was measured at 48 months postnatal. Hierarchical linear modeling was used to test main effects and interactions of parents’ symptoms predicting child cortisol, controlling for birth mother cortisol (inherited risk). Prenatal exposure to birth mother symptoms predicted lower child cortisol (main effect), as did postnatal exposure to adoptive parent symptoms (interaction effects). Adoptive mother 9-month symptoms exacerbated cortisol-lowering effects of both concurrent paternal symptoms and later (27-month) maternal symptoms, and the effect of birth mother cortisol. Lower child cortisol, in turn, was associated with higher child internalizing symptoms. Implications are discussed with respect to the intergenerational transmission of depression risk.