I n a cohort of 18,500 newborn infants, those who had experienced one or more convulsions were studied. Data were available for the unaffected as well as for the affected children. All families were members of a prepaid medical care program that provides comprehensive medical care.By five years of age, two percent of the 18,500 children had had one or more febrile convulsions; one percent had had nonfebrile convulsions. The incidence of the first nonfebrile seizure was highest during the first month of life; febrile convulsions reached a high peak during the second year of life.The risk of a febrile convulsion was equal for boys and girls but that of a nonfebrile seizure was higher for boys. The nonfebrile group had an excess of children with birth weights between 1500 and 2500 g, especially those whose gestational age was 37 weeks or more. The distribution by birth weight and gestational age of the febrile group was similar to that of the entire cohort.Multiple episodes occurred in one-third of the children of the febrile group and in three-quarters of the nonfebrile group. About 3 % of the children with febrile seizures later developed nonfebrile convulsions; about 7% of the nonfebrile group had initially a febrile seizure. Nearly 31 % in the nonfebrile group and 7 % in the febrile group had severe congenital anomalies; in the entire cohort only 3 % had such an anomaly before they reached age five. Among the children in the nonfebrile group were 10% with cerebral palsy and 16% with mental retardation including 5 % with both disorders. SpeculationAs the cohort of 18,500 children grows older, a certain number of them will develop real epilepsy. This study provides three distinct groups: children who had febrile convulsions, those who had nonfebrile convulsions, and those who had no seizures in early childhood. The future follow-up of these groups will provide the necessary data for determining the relative rates of developing epilepsy associated with the convulsion experience in early childhood.