Febrile infection-related epilepsy syndrome (FIRES) is a rare but devastating condition of the children and only a few adults with similar clinical conditions have been reported so far. Two female patients in their thirties presented with explosive onset of intractable epilepsy induced by fever followed by cognitive problems and they were diagnosed as "limbic encephalitis" in the beginning. However, neither paraneoplastic nor infectious etiology was detected despite detailed investigations. Their video-EEG monitoring showed multifocal origin of epileptic activity consistent with childhood series of FIRES. PET studies showed bilateral mesial temporal and frontal lobe hypometabolism, respectively. Many antiepileptic drugs and relevant immunotherapeutics were not able to control their seizures. Furthermore, ketogenic diet did not provide prominent benefits after this delay in the diagnosis of FIRES in adult patients.