Five neonates born to women who had had varicella late in pregnancy or in the post-partum were admitted to our unit during the last year. In utero transmission of varicella-zoster virus occurred in 2 cases. One of them had no clinical eruption but specific IgM at a titer of 1/200. The mother presented with varicella 15 days before delivery. The other developed severe neonatal congenital varicella (with disseminated eruption, pneumonia and seizures). She was treated by Aciclovir (15 mg/kg/8 h). The mother presented with chickenpox 24 hours after birth. Varicella occurring in a pregnant woman from 4 days before to 2 days after delivery is dangerous because the baby will lack maternal antibodies. It may develop severe neonatal varicella (mortality: 20-30%). A neonate in critical condition was successfully given a prophylactic treatment by Aciclovir IV (15 mg/kg/8 h for 5 days) and varicella-zona immunoglobulins (2 ml on days 1, 2, 3). This approach may be the best treatment for babies at risk for severe neonatal varicella.