A family history of seizures, preexisting brain damage, or birth complications may modify the long-term risk of epilepsy after febrile seizures. The authors evaluated the association between febrile seizures and epilepsy in a population-based cohort of 1.54 million persons born in Denmark (1978-2002), including 49,857 persons with febrile seizures and 16,481 persons with epilepsy. Overall, for children with febrile seizures compared with those without such seizures, the rate ratio for epilepsy was 5.43 (95% confidence interval: 5.19, 5.69). The risk remained high during the entire follow-up but was particularly high shortly after the first febrile seizure, especially in children who experienced early (3 years of age) onset of febrile seizures. At 23 years of follow-up, the overall cumulative incidence of epilepsy after febrile seizures was 6.9% (95% confidence interval: 6.5, 7.3). In conclusion, persons with a history of febrile seizures had a higher rate of epilepsy that lasted into adult life, but less than 7 percent of children with febrile seizures developed epilepsy during 23 years of follow-up. The risk was higher for those who had a family history of epilepsy, cerebral palsy, or low Apgar scores at 5 minutes.