In a population of 850,000, the authors studied afebrile seizures that follow febrile seizures. Review of all paediatric EEGs identified 504 children with epilepsy beginning between 1977 and 1985. Follow-up averaged 85 months. 14.9 per cent had preceding febrile seizures: 13 per cent complex partial, 13 per cent partial/secondary generalized and 22 per cent generalized tonic-clonic. The rate of preceding febrile seizures did not vary with the cause of epilepsy. Prolonged febrile seizures were not associated with any particular afebrile seizure type. Of 17 with preceding prolonged febrile seizures, seven developed intractable epilepsy: 17.9 per cent of the total intractable cases. Only two developed idiopathic intractable complex partial seizures after prolonged febrile seizures. The authors conclude that febrile seizures most often precede generalized tonic-clonic afebrile seizures. Prolonged febrile seizures rarely precede idiopathic intractable complex partial seizures. The febrile seizure tendency may be a fundamental marker of an individual's seizure threshold.