Herpes simplex virus (HSV) infections are among the infections most frequently encountered by humans. Two types of HSV infections have been identified-HSV-1, which usually causes orolabial disease, and HSV-2, which is associated more frequently with genital and newborn infections. Usually, HSV causes mild and self-limited disease of the mouth and lips or at genital sites. However, on occasion, the disease can be life-threatening. Such is the case with neonatal HSV infection and HSV infections of the central nervous system. Furthermore, in the immunocompromised host, severe infection has been encountered and is a source of morbidity. Even in the immunocompetent host, frequent recurrences, particularly those of the genital tract, can be debilitating. Because HSV does cause genital ulcerative disease, it is associated with an increased risk of acquiring a human immunodeficiency virus infection. During the past 2 decades, selective and specific inhibitors of HSV replication have been developed. These agents, acyclovir, valaciclovir, and famciclovir, all accelerate the events of healing and decrease the probability of excreting the virus when they are taken in a suppressive fashion. The long-term safety of acyclovir has been unequivocally established. Its prodrug, valaciclovir, and the prodrug of penciclovir, famciclovir, have not been used in practice as long and, therefore, less is known about these agents; however, neither is available as a pediatric formulation.