The risk of recurrence after an initial febrile seizure was 25% in a population-based cohort of 639 children followed from their first febrile seizure. Prognostic factors were an increasing risk of recurrence with younger age at first febrile seizure, a first degree relative with febrile seizures and complex features of the first febrile seizure. The effect of complex features was modified by age at first febrile seizure and family history in that complex features alone did not increase risk of recurrence but further increased the risk for children under 18 months at first seizure and/or with a positive family history. The prognostic factors for all febrile convulsions recurrences were also prognostic for having subsequent complex febrile convulsions. Children with none of the prognostic factors had only a 3% risk of a future complex febrile seizure while children under 18 months at first febrile convulsion and a positive family history or complex features had about a 20% risk of a subsequent complex febrile seizure.