Respiratory syncytial virus (RSV) is an RNA virus that causes respiratory tract infections in children. In the North- ern Hemisphere, the peak infection season is November through April. By two years of age, most children will have had an RSV infection. Bronchiolitis, a lower respiratory tract infection, is often caused by RSV. An RSV infection is diagnosed based on patient history and physical examination. Children typically present with cough, coryza, and wheezing. Laboratory testing and chest radiography are not necessary to make the diagnosis. Serious concur- rent bacterial infections are rare. Treatment of an RSV infection is supportive, with particular attention to maintaining hydration and oxygenation. Children younger than 60 days and those with severe symptoms may require hospitalization. Neither antibiotics nor corticosteroids are helpful for bronchiolitis. A bronchodilator trial is appropriate for children with wheezing, but should not be continued unless there is a prompt favorable response. Frequent hand washing and contact isolation may prevent the spread of RSV infections. Children younger than two years at high risk of severe illness, including those born before 35 weeks of gestation and those with chronic lung or cardiac problems, may be candidates for palivizumab prophylaxis for RSV infection during the peak infection season. Most children recover uneventfully with supportive care.