Acute bronchiolitis is defined as viral-induced inflammation of bronchioles. The clinical manifestations occur as a consequence of airway inflammation and air trapping. Bronchiolitis most commonly occurs as an acute illness in children younger than 2 years of age. The most frequent cause is rhinovirus or respiratory syncytial virus (RSV) infection, other respiratory viruses being less common (Table I). The illness is generally self-limiting. Patients often feed poorly and have mild upper respiratory tract infection (URTI) signs, low-grade fever, hyperinflation of the chest and wheezing. Symptoms of severe illness include tachypnoea and lower chest wall retractions. (1) Bronchiolitis must be differentiated from aspiration of a foreign body, in which URTI signs are lacking.