Inclusion Criteria:

• * Signed informed consent from parent(s) or legal guardian(s)
• * Confirmation of HSV infection from surface culture/PCR, skin lesion culture/PCR, blood PCR, or CSF PCR (performed at UAB Virology lab)
• * ≥34 weeks gestational age at birth
• * Weight at study enrollment is ≥ 2000 grams
• * Receiving intravenous acyclovir, prescribed by the patient's physician for ≤ 14 days
• * ≤ 42 days of age at initiation of parenteral acyclovir
• * Creatinine ≤ 1.2

Exclusion Criteria:

• * Imminent demise
• * Current receipt of other investigational drugs
• * Major congenital anomaly that in the site investigator's opinion may impact drug metabolism or the patient's volume of distribution
• * Creatinine of \> 1.2 prior to initiation of valacyclovir
• * Evidence of immunosuppression (HIV infected, immune deficiencies, etc.)
• * Any condition that, in the opinion of the investigator, would place the subject at an unacceptable injury risk or that may interfere with successful study completion
• * \> 42 days of age at initiation of parenteral acyclovir
• * Concern for parental/guardian compliance