Herpes simplex virus (HSV) infections of the central nervous system are a significant cause of mortality and morbidity. The introduction of antiviral therapy has improved the outcome for patients with life-threatening disease. Neonatal HSV infection is usually acquired at the time of delivery by contact of the fetus with infected maternal genital secretions resulting in disease that can be localized to the skin, eye, and mouth, and can lead to encephalitis or become disseminated. A total of 291 babies with neonatal HSV infection have been evaluated over a period of 14 years with mortality and morbidity rates determined at one year. Vidarabine therapy decreased the incidence of mortality and improved morbidity rates; however, further improvement in mortality rates with acyclovir therapy has not been apparent. No significant clinical toxicity appeared in either treatment group. In order to improve outcome, earlier intervention and prophylactic strategies must be developed. For patients with herpes simplex encephalitis, acyclovir therapy is superior to vidarabine therapy for biopsy-proven disease. When outcome is compared for 136 vidarabine- and 46 acyclovir-treated, biopsy-proven patients, mortality rates are decreased to 20 percent with acyclovir, and approximately 40 percent of survivors are evaluated as normal at one year after therapy. Despite better outcome with antiviral therapy for the treatment of biopsy-proven herpes simplex encephalitis, further improvement is required.