Although herpes simplex virus (HSV) infections are common in pregnant women, they are rarely serious. The complication, however, is viral transmission to the infant and morbidity and mortality in neonatal herpes remains considerable, in spite of the availability of antiviral therapy. Early recognition and treatment of the infected child is of the utmost importance to inhibit viral replication and thus limit the severity of the disease. Moreover, prevention is the ultimate challenge. Unfortunately, in many cases this is not achievable since the infection in the mother and child often presents without typical herpes symptoms. This was illustrated in a follow-up study of neonatal herpes in Sweden. In nearly half of the cases of neonatal herpes, neither mother nor child had typical herpes symptoms. The herpes simplex virus type 2 (HSV-2) infections were more often atypical or asymptomatic in nature in the mother and child than the HSV-1 infections. Outcome was more serious in HSV-2 infections, and a large proportion of children with this type did not have skin lesions. Neonatal herpes transmitted from recurrent maternal infection had a long incubation period (mean 14 days) and was often localized to the brain. Disease due to primary infection was disseminated, with a mean incubation time of 6 days. Preventive strategies are discussed. In the majority of cases, clinical recognition of risk factors for transmission in the mother--a prerequisite for preventive measurements --is not possible.