This report focuses on the relationship of placental pathology to unfavorable pregnancy outcome. Relevant literature is cited and data from the author's investigations are reported and tabulated. The reader will find detailed information on placental lesions that have not been completely investigated or discussed previously. Particular considerations include placental meconium staining, edema, acute and chronic intrauterine infections, placental fetal vasculopathy with fetal nucleated red blood cells, and chorangiosis or other placental dysmaturity. These pathologic changes often signify the pathogenesis of cerebral palsy and other developmental disorders. Almost 90% of neurodevelopmental disorders are initiated before the intrapartum period. Prenatal asphyxia or severe chronic fetal hypoxia are probably present therein. Most investigations of these afflictions are invalid because they do not include placental study with well-designed epidemiologic methods. The pathologic placental findings that are most strongly associated with perinatal asphyxia include chronic ischemic changes, fetal nucleated red blood cells, intravillous hemorrhage, fetal fibrin vascular intimal cushions, meconium staining, and placental intervillous fibrin. Chorioamnionitis is a pathologic entity rather than a clinical syndrome as defined by obstetricians. When it causes severe prematurity, chorioamnionitis is also associated with cerebral palsy.