Central nervous system herpes simplex virus infection is suspected in patients presenting with acute-onset seizures and lethargy. The potential neurologic sequelae from untreated herpes infection can prompt empirical acyclovir therapy, even in afebrile subjects. The objectives of this study were to determine the frequency of central nervous system herpes simplex virus infection in children presenting with afebrile seizures and to assess the need for empirical acyclovir therapy. Clinical and laboratory data of children with acute-onset afebrile seizures and children with central nervous system herpes simplex virus infection were compared. Polymerase chain reaction and viral cultures of the cerebrospinal fluid for herpes simplex virus infection were negative in all subjects with afebrile seizures; 32.7% of these subjects were empirically treated with acyclovir. In conclusion, central nervous system herpes simplex virus infection is uncommon in children presenting with afebrile seizures, and acyclovir therapy is rarely necessary in subjects with normal neurologic examination and cerebrospinal fluid analysis.