Viral encephalitides include acute viral encephalitis, post-infectious encephalomyelitis, viral infections of the central nervous system (CNS), and chronic degenerative diseases. This chapter presents the diagnostic and clinical challenges that accompany the management of seizures following CNS infection by the herpes viruses, RNA viruses, enteroviruses, and arenaviruses. Fever, headache, lethargy, nausea, and non-specific flu-like symptoms are often the first clinical signs of infection, with subsequent symptoms of leptomeningeal irritation becoming prominent. Specific viruses can now be detected in the cerebrospinal fluid (CSF) using polymerase chain reaction (PCR) where previously specific viral diagnoses could only be made by brain biopsy. Patients should therefore be treated with acyclovir if the clinical suspicion is high pending final herpes simplex virus (HSV)-1 PCR results, and repeat CSF testing should be considered. Wider applications of PCR may help to determine individual risks for some of the more common viral agents.