The incidence rates of epileptic seizures and epileptic seizures with centrotemporal (Rolandic) discharges were found to be 134/100,000 and 21/100,000, respectively. These were determined in an epidemiological study in a population consisting of 52,252 children aged 0-15 years in a county in the northern part of Sweden. Epileptic seizures with Rolandic discharges represented about 16% of all the epileptic seizures (febrile convulsions not included). They were four times more common than classic petit mal with 3/sec spike-and-wave activity.