Although fever is regarded as the main trigger in the pathogenesis of febrile seizures (FS), it is not supposed to be the unique causative factor. In FS, there is a strong familial predisposition. This does not exclude infections as a causative factor because subtle genetic polymorphisms have been demonstrated to affect the course of infections. We review the literature on: (1) the role of fever, especially the height of temperature, its cause, and metabolic effects induced by temperature; (2) the role of heredity; (3) the role of cytokines which play a role in the induction of fever; and (4) the role of type of infection, with emphasis on newly identified agents and improved diagnostic techniques. With modern molecular techniques such as PCR, viruses have been detected in the CSF far more often than previously thought, even in the absence of pleocytosis of the CSF. This makes it difficult to distinguish FS from acute encephalitis. FS may be caused by neuroinvasion or intracerebral activation of viruses. Further studies should focus on these options because therapeutic intervention is possible and may prevent late sequelae such as recurrent FS and subsequent epilepsy.