In order to assess the effects of the onset and chronicity of maternal depression on neonatal physiology, eighty pregnant women were assessed for depression during mid-pregnancy (M gestational age = 25.9 weeks) and shortly after delivery. The women were classified as reporting depressive symptoms 1) only during the prepartum assessment; 2) only during the postpartum assessment; 3) during both the prepartum and postpartum assessments; or 4) reporting no depressive symptoms at either the prepartum or the postpartum assessment. Maternal mood and biochemistry were assessed during pregnancy, and the EEG and biochemical characteristics of their 1-week-old infants were assessed shortly after birth. As predicted, the newborns of the mothers with prepartum and postpartum depressive symptoms had elevated cortisol and norepinephrine levels, lower dopamine levels, and greater relative right frontal EEG asymmetry. The infants in the prepartum group also showed greater relative right frontal EEG asymmetry and higher norepinephrine levels. These data suggest that effects on newborn physiology depend more on prepartum than postpartum maternal depression but may also depend on the duration of the depressive symptoms.