During the transition to motherhood, women typically show favorable psychological adjustment after the first child is born, whereas 10 percent to 26 percent of women are at risk of developing clinically significant postpartum depressive symptoms. Little is known about which individuals are especially protected against the emergence of postpartum depressive symptoms during this time. Using a "risk and resilience" theoretical framework, we expected that optimism during pregnancy would be associated with less postpartum depression severity, controlling for antenatal depressive symptoms. We also predicted that optimism would buffer the relations between four dimensions of stress frequency during pregnancy (financial, spousal, physical, and occupational) and the development of postpartum depressive symptoms. Using data from three panels of a longitudinal study of married couples across the transition to first parenthood, we found that optimism of expectant mothers during pregnancy was associated with decreased depression severity at six months and 12 months postpartum. The data also showed that when women experienced high frequencies of financial, spousal, and physical stress during pregnancy, those who were optimistic were much less at risk of developing clinically significant depressive symptoms at six months and 12 months postpartum compared with those who were pessimistic. Implications for enhancing optimism across the transition to motherhood through culturally relevant social work practice are discussed.