In the EPGP study, only 15% had no developmental delays at follow-up, although another 15% had only mild delays. Overall, this would be 30% with good developmental outcome and not significantly different than previous reports. Furthermore, this includes the 15 patients for whom a genetic cause was identified; 14 of these had severe delays. Predictors of developmental disability were nearly identical to those for subsequent seizures. However, shorter time from IS onset to treatment and the use of first-line medication were predictors of IS freedom but not predictors of developmental outcomes. This most important predictors of good developmental outcome were older age at IS onset, normal development prior to IS, and IS freedom after first medication.