We report on a 12-year-old boy with herpes simplex encephalitis, in whom a severe localised skin reaction developed following the infusion of intravenous acyclovir. Oral valaciclovir was given as continuation therapy to complete the 3-week course of antiviral treatment and resulted in complete recovery without side effects. This report illustrates the advantage of using the polymerase chain reaction to diagnose herpes simplex encephalitis and the potential use of newer antiviral agents, such as valaciclovir, as continuation therapy in the management of the infection. The higher oral bioavailability of newer antiviral agents allows part of the extended treatment period of patients with herpes simplex encephalitis to be carried out as an ambulatory oral regimen.