At birth the immune system of a neonate is immature and viruses can cause severe infections. Since the signs and symptoms of postnatal viral diseases can be identical to those in bacterial infections, viral diseases are often treated with antibiotics. Any infant with signs of serious infections, in whom no bacteria are found, should be suspected for a viral infection. Prevention of transmission of viruses and cohorting of infected infants should be practiced in NICUs. Since postnatal viral infections can have a long-term impact on the health in a child, all effective preventive and curative interventions should be utilized.