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The National Institutes of Health (NIH) defines febrile seizure as an event in infancy or childhood usually occurring between 3 months and 5 years of age associated with a fever but without evidence of intracranial infection or defined cause for the seizure. The International League Against Epilepsy (ILAE) further refined the definition to include infants older than 1 month of age without prior neonatal seizures or unprovoked seizures who did not meet criteria for acute symptomatic seizures. Febrile seizures occur in approximately 2% to 5% of infants and young children in the United States and as many as 9% to 14% of children in Japan, India, and Guam, rendering it the most common neurologic disorder in this age group and the most common type of convulsive event in children younger than 5 years of age.


Febrile seizures are defined by the age of the patient at presentation and the clinical context in which they occur. Febrile seizures can occur in children age 1 month to 6 years, with a peak incidence at 18 months old. Ninety percent of children with febrile seizures will have their first event prior to reaching the age of 3 years. Alternate diagnoses should be considered in individuals who present after this age.

Febrile seizures occur in association with a temperature of greater than 38°C (100.4°F) prior to or shortly after the event. The seizures often happen very early in the course of illness, and there may not be a history of preceding fever.

A diagnosis of febrile seizures is excluded if the affected child has a prior history of afebrile seizures, or if the seizure occurs in the context of a central nervous system infection or acute metabolic abnormality that can cause seizures.


Febrile seizures are classified as either “simple” or “complex” based on clinical features including semiology, duration, and frequency (Table 551-1). These classifications are important as they guide the diagnostic workup and have prognostic implications. The majority of febrile seizures are simple febrile seizures, which are generalized seizures lasting < 15 minutes in duration that occur only once in a 24-hour period. They usually last < 5 minutes and consist of clonic movements, although atonic or tonic seizures are sometimes seen. Postictal drowsiness usually resolves within 5 to 10 minutes depending on the duration of the seizure.


Conversely, 20% to 30% of febrile ...

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