The medical records of 68 children who had had infantile febrile status epilepticus (FSE) were examined. Follow-up periods ranged from three to 28 years (mean 8 years 10 months). Details were abstracted of relevant medical events prior to FSE, diagnosis of the febrile illness, age at onset and main characteristics of FSE, and outcome (subsequent febrile convulsions and/or epilepsy, neurological and psychiatric disorders). Neither medical events prior to FSE nor aetiology of fever were associated with subsequent febrile convulsions, epilepsy, or neurological or psychiatric abnormalities. There was a significant association between age at onset of FSE and both subsequent epilepsy and CNS disorders. 12 of the 13 children who had had transient or persistent post-ictal hemiparesis subsequently developed epilepsy. Of the 46 children who later developed epilepsy, 34 had partial seizures and 12 had generalized seizures. The latter were more common among children who had had FSE before the age of one year. Likewise, all those who developed severe myoclonic epilepsy in infancy had their first FSE before age one. These findings suggest that age at onset of FSE is the most important feature determining long-term outcome.