Of 63 patients suffering a single attack of acute bronchiolitis in infancy, 16 (25.4%) were found to have bronchial asthma on follow-up 4 to 14 years later. The familial incidence of allergic manifestations was high (62%) in this group. Thirteen patients (20.6%) continued to have attacks of wheezing associated with respiratory infections. This tendency to wheeze gradually subsided after an average period of five years. The ultimate prognosis of these children is not known. The presence of a positive immediate family history of allergy in an infant with bronchiolitis considerably alters the usually excellent prognosis. The first attack of bronchiolitis may be a form of respiratory allergic manifestation in an already potentially asthmatic infant.