Herpes simplex infections of the nervous system.Dramatic progress has been made recently in diagnosing and treating herpes simplex virus encephalitis (HSVE). Advances in imaging technology have greatly enhanced our ability to diagnose the illness noninvasively. Acyclovir is of proven efficacy and is generally well-tolerated. The major clinical management problem is that the pathologic process in the brain is usually well-advanced before the patient presents, and the symptoms, particularly in newborns or infants, are often initially nonspecific. This, plus a too frequent failure to recognize the nature and seriousness of the process, results in further delay in diagnosis and treatment. Physicians need to develop an increased awareness of the early signs and symptoms of the presentation of HSVE, and of the imperative for early treatment.