Given the dependence of the fetus on adequate placental function, one might predict that specific placental lesions would be associated with distinct pregnancy outcomes. To test this hypothesis, we examined 609 nontwin placentas and explored the relationship between histologic diagnosis and the following variables: gestational age at delivery, placental size, and selected categories of clinical disease. Five separate patterns of placental injury were examined. Two lesions were particularly frequent prior to 37 weeks' gestation: increased intervillous fibrin, which was most common in early preterm placentas (20 to 31 weeks), and membrane hemosiderin, which was increased in both early and late preterm placentas (32 to 36 weeks). Three lesions--maternal vasculopathy, villitis of unknown etiology, and increased intervillous fibrin--were associated with retarded fetal and placental growth. Only maternal vasculopathy was significantly increased in placentas from pregnancies with gestational hypertension, while two other lesions--villitis of unknown etiology and increased intervillous fibrin--were appreciably increased with nonhypertensive chronic antenatal abnormalities.