Acute bronchiolitis due to viral agents (RSV, parainfluenza, influenza, adenovirus) is a relatively frequent disease of infancy. Seasonal epidemic pattern have been recognized, and nosocomial infections in pediatric wards occur. Until age 2 years most children have experienced some form of airway disease attributable to RSV. Some patients require hospital treatment; about 15% of our patients had to be transferred to the intensive care unit. Bronchiolitis seems to be frequently the first manifestation of asthma and we found higher IgG antibody titers to viruses causing bronchiolitis in children with asthma than in controls. Retrospective analysis of the charts of 147 cases of bronchiolitis revealed considerable uncertainty regarding therapeutic concepts. Mainstays of conservative therapy include oxygen, adequate hydration (often IV), and sometimes bronchodilators (based on the clinical impression of effectiveness in the individual patient). Mist therapy and secretolytic agents remain popular, although no clinical effect has been demonstrated. Attention should be directed toward the relief of upper airway obstruction caused by swelling, secretions, and nasogastric tubes. Oxygen administration in infants with coexisting chronic airway disease (e.g., BPD) and bronchiolitis may cause CO2 retention. Bronchodilators can cause hypoxia and increase bronchial compressibility by reducing smooth muscle tone. However, in severe cases a trial under pulse oximetry control seems worthwhile. Steroids seem to bring no clinical improvement, except in infants with protracted wheezing after bronchiolitis and patients with preexisting BPD.