Respiratory syncytial virus is a major cause of lower respiratory tract infections in infants and young children. It is prevalent worldwide and affects all age groups, but severe lower respiratory tract infections primarily occur in early neonatal period (up until 6 months of age), premature infants, in children with chronic lung disease as well as children with congenital heart defects. Most children overcome the primary infection up until the age of two. However, due to viral antigen heterogeneity, reinfections can occur throughout the entire lifespan, but then disease is milder than in infancy. Amongst the younger population, most of the infections occur in the lower respiratory tract where the infection will clinically appear as bronchiolitis or pneumonia. In comparison, in older children and adults the infection will most commonly manifest as a mild upper respiratory tract infection. The virus regularly appears every year either as big or small epidemics, which correlate in the moderate climate belt, during winter and early spring. The appearance of an epidemic is followed by an increased number of hospitalization of infants and small children due to respiratory diseases. The ones who are at increased risk of developing exceptionally severe form of the disease accompanied by high morbidity and mortality are premature infants, children with chronic lung diseases and children with congenital heart defects. For this reason the before mentioned groups are included in the so called population at risk. Due to nonexistence of etiological and restricted supportive therapy, there are now efforts worldwide to produce an appropriate vaccine that would prevent development of infection as well as protect the population at risk. However, in the meantime some parts of the world have resorted to an alternative, passive form of protection for the population at risk of the RSV; immune prophylaxis with palivizumab whose positive effects are yet to be graded.