Fifty-one infants admitted to hospital because of acute bronchiolitis were followed until 2 years of age. Sixty per cent had three or more attacks of bronchopulmonary obstruction, and the remainder two or less attacks. The children with three or more attacks also had more respiratory infections. They had younger parents and their close relatives more often had respiratory atopic illness. The children with three or more attacks wheezed for a longer time after the bronchiolitis. No difference was found for breast-feeding, neonatal respiratory complications, crowded homes, parental smoking and other social factors. To detect children at risk of recurrent obstructive airways disease after bronchiolitis, a discriminant analysis was performed. The discriminant function classified 28 of the 31 children with recurrent obstructive episodes as belonging to the risk group, and 18 of the 20 children with two or less episodes to the non-risk group.