To reassess the relations between postulated risk factors and seizure recurrence after a first febrile seizure (FS), the individual data from five follow-up studies that used similar definitions of FSs and risk factors were pooled and reanalyzed. The risk of frequent recurrent seizures and of the occurrence of complex seizures in previously healthy, untreated children was studied. Seizure recurrence hazard was described as a function of the child's attained age. The influence of various risk factors on the recurrence hazard was assessed, with control for other factors. Of a total of 2496 children with 1410 episodes of recurrent seizures, 32% had one, 15% had two, and 7% had three or more recurrent seizures after a first FS; 7% had a complex seizure. The hazard of recurrent seizures was highest between the ages of 12 and 24 months. After a first and a second recurrence, the risk of further FSs was two and two and one-half times higher, respectively. A history of febrile or unprovoked seizures in a first-degree family member and a relatively low temperature at the time of the first seizure were also associated with an increased risk of subsequent recurrences. Young age at onset (< 12 months), a family history of unprovoked seizures, and a partial initial FS were all associated with an increased risk of complex seizures. A higher recurrence rate in clinic-based studies compared with population-based studies could not be explained by a difference in the presence of the risk factors studied. Thus other factors must influence seizure recurrence after an initial FS.