Herpes simplex virus infection of the central nervous system is still a significant cause of morbidity and often mortality. Changes of central nervous system are results of primary infection or activation of latent HSV-1, HSV-2. Neurological deficits often follow encephalitis herpetica. The application of PCR is prompt and specific diagnosis of herpes simplex virus infections of the brain. Advances in treatment herpes simplex encephalitis with acyclovir have improved outcome.