We analyzed the gestational, parturitional, neonatal (GPN) histories of 281 severely mentally retarded patients with cerebral palsy to define the etiology or pathogenesis of cerebral palsy in each patient. No association between type of cerebral palsy and GPN histories was found except for an increase in spastic-athetoid patients in the breech delivery subgroup. Significant findings include: increased incidence of prematurity and postmaturity, small and large for-gestational age (GA) fetal size, a normal birthweight for GA distribution of patients with diabetic mothers, an excess of mothers greater than or equal to 35 and less than or equal to 20 years old, an increased immediately-previous sib interval of 2.59 years suggestive of an "infertility factor", an unremarkable GPN history in one third of the cases, in another one third GPN problems not usually associated with a high risk of CNS damage, and in one third gross complications which were probably responsible for the CP, including: an increased incidence of breech deliveries, twinning, prolonged and precipitous labor and placental complications; no increased association of athetosis and Rh incompatibility or incidence of toxemia was found. Disseminated intravascular coagulation due to prenatal death of a twin may have been the cause of brain damage in several patients.