Acute bronchiolitis is the most common severe lower-respiratory-tract infection of infancy. Although signs and symptoms may become severe, most viral respiratory infections are self-limited and improvement occurs within a few days. Patients hospitalized with bronchiolitis usually require supportive therapy, including oxygen and fluids, and may require mechanical ventilation. A trial of aerosolized beta 2-agonist is warranted in patients with bronchiolitis. Systemic corticosteroids have not been proved efficacious. Inhaled corticosteroids may be useful in reducing the severity of chronic wheezing that may follow acute bronchiolitis. Ribavirin may be considered in patients with severe disease of those at high risk for severe disease.