A febrile seizure, also known as a fever fit or febrile convulsion, is a seizure associated with an increased body temperature but without any intracranial infection. Febrile seizures affect 2–7% of children and are more common in boys than girls. They most commonly occur in children between the ages of 6 months and 5 years with a higher incidence around 18 month of age. Most seizures last less than five minutes, and the child typically recovers quickly.

There are two types of febrile seizures: simple and complex. Simple febrile seizures involve an otherwise healthy child with a single, one episode of generalized seizure lasting less than 15 minutes. Complex febrile seizures have one of more of the following: focal symptoms such as jerking of only one side of the body, duration greater than 15 minutes, or two or more seizures within 24 hours. About 60–70% are classified as simple febrile seizures and 30–40% complex.

Febrile seizures are triggered by fever, typically due to a viral infection. The underlying mechanism is not fully known, but it is thought to involve genetics, environmental factors, brain immaturity, and inflammatory mediators. The rapid rise and decrease of the body temperature is not the main mechanism for febrile seizure occurrence. The diagnosis involves verifying that there is not an infection of the brain, and there have not been prior seizures without a fever. Blood testing, imaging of the brain, or an electroencephalogram (EEG) are typically not needed. Examination to determine the source of the fever is important. In otherwise healthy-looking children, a lumbar puncture is not necessarily required.

After a single febrile seizure there is an approximately 35% chance of having another one during childhood. Neither anti-seizure medication nor anti-fever medication are recommended in an effort to prevent further febrile seizures. Efforts to rapidly cool the child’s body during a seizure have not been extensively studied but are not recommended. The long-term outcome of children with febrile seizures is generally excellent with similar academic achievements to other children. There is strong evidence that children with febrile seizures have a slightly increased risk of epilepsy at 2–3% compared to the general population risk of about 1%.