Bronchiolitis is an acute inflammation of the airways. In infancy, it usually results from viral infection, with RSV the most common agent. The clinical syndrome is characterized by symptoms of lower respiratory tract infection and obstruction. In most patients, the duration of illness is 1 week, but bronchiolitis can cause serious morbidity in patients with pre-existing cardiopulmonary disease. In addition, patients may be left with serious sequelae, including PBAR and OB. RSV causes direct damage to airways, but an exaggerated host immune response may contribute to the pathogenesis of airway obstruction in bronchiolitis. The mainstays of therapy include oxygen supplementation and fluid resuscitation, and other modalities remain controversial. There are no studies to support the use of corticosteroids alone in the treatment of bronchiolitis, but several recent reports demonstrate the value of bronchodilator therapy in some patients. Antiviral agents such as ribavirin show great promise in a therapy for bronchiolitis. In addition, ribavirin may modify some aspects of the immune response during acute infection with RSV, and therefore may play a role in the prevention of long-term sequelae.