We studied 244 patients (of all ages) who presented with a first unprovoked seizure and were followed for a median of 22 months in order to ascertain the risk of subsequent seizures. The cumulative risks of recurrence were 16 per cent at 12 months, 21 per cent at 24 months, and 27 per cent at 36 months after the initial seizure. The risk of recurrence in patients with a history of prior neurologic insult was 34 per cent; all recurrences in this group were observed within the first 20 months. Only 17 per cent of patients without such a history (classified as idiopathic) had a recurrence by 20 months; recurrence in this group was 26 per cent by 36 months. Patients with no recurrence for 36 months did not have a recurrence after that time. Among idiopathic cases the risk of recurrence was increased in patients with generalized spike-wave electroencephalograms (50 per cent at 18 months) and in those who had a sibling with seizures (35 per cent at four months). Age at first seizure, sex, seizure type, onset with status epilepticus, or abnormality on neurologic examination did not affect the risk of recurrence.