It is known that the localized form of herpes simplex virus (HSV) infection does not always show a good prognosis. A preterm infant who evidenced skin and tongue lesions, caused by HSV type 1, was treated by acycloguanosine. The result was satisfactory without any complications. Therefore, a localized form of HSV infection of the newborn infant, even though the patient has a low-birth-weight, should be treated by the drug immediately after the observation of the positive HSV culture.