Respiratory syncytial virus (RSV) is the leading cause of lower respiratory disease in young children in both developing and developed countries. By age 2, nearly all children have been infected by RSV.The clinical manifestations range from mild upper respiratory symptoms to bronchiolitis and pneumonia. First infections are nearly always symptomatic and frequently cause lower respiratory tract disease, whereas subsequent infections are generally milder. Although children with underlying conditions such as prematurity, chronic lung disease, congenital heart disease, and immuno-suppression are at high risk for severe disease, many children without underlying conditions require hospitalization. Treatment is supportive. Immunoprophylaxis with palivizumab or RSV immune globulin may benefit children born prematurely, especially those with bronchopulmonary dysplasia. To date, the development of an effective vaccine has been unsuccessful.