The pathogenesis of perinatal death due to placental infarction was analyzed in a large prospective study that included more than 1000 medical, demographic, hereditary, and postmortem variables. The disorder was the fifth most frequent cause of death in the study with a perinatal mortality of 2.26/1000 births. Its frequency was directly correlated with the gravidas' blood pressures, an effect augmented by albuminuria and work during pregnancy. Fatal infarcts were increased 20-fold with glomerulonephritis, fivefold with abruptio placentae, and twofold when the gravidas' hemoglobins were over 12 g/100 ml. Maternal weight gains were suboptimal and the involved neonates had a pattern of growth retardation characteristic of undernutrition. The disorder was more frequent when the gravida had made few prenatal visits for medical care and had had prior unsuccessful pregnancies.