Herpes simplex virus infections of the central nervous system remain a significant cause of morbidity and mortality, in spite of safe and efficacious antiviral therapy. Advances in the treatment of neonatal herpes and herpes simplex encephalitis with acyclovir have improved outcome. The application of polymerase chain reaction has allowed for the prompt and specific diagnosis of herpes simplex virus infections of the brain. This review summarizes our current knowledge on the pathogenesis, diagnosis, and treatment of herpes simplex virus infections of the brain. Opportunities for the future will be defined. © 1995 by The University of Chicago. All rights reserved.