The purpose of this study is to test whether long-term treatment with oral acyclovir improves the outcome for infants with herpes simplex virus (HSV) disease of the skin, eyes, and mouth (SEM). Study participants will include infants in the United States and Canada who have HSV disease of the skin, eyes, and mouth, with no central nervous system disease present. Initially, all subjects will be treated with acyclovir administered through IV access (through the vein) for 14 days while hospitalized. Participants will then be placed in one of two groups, acyclovir given by mouth or a placebo (substance with no medication present). The participant and the study site will not know to which group the subject is assigned. All children will be followed at 6, 12, 24, 36, 48, and 60 months of age. During the follow up visits, physicals, hearing assessments, eye assessments, and neurological assessments will be completed.