In the present cohort, 85% of infants hospitalized for wheezing outgrew their symptoms until puberty, but 30-40% had asthma, depending on criteria, again in young adulthood. The aim of this study was to determine early predictors for adulthood asthma, bronchial reactivity, and lung function abnormalities in infants hospitalized for bronchiolitis. Fifty-two children hospitalized for bronchiolitis at < 2 years of age were restudied at the median age of 19 years. Wheezing histories and early risk factors for later asthma were recorded prospectively during infancy. The follow-up study consisted of a written questionnaire, physical examination, flow-volume spirometry, methacholine inhalation challenge, home peak expiratory flow monitoring, and skin-prick tests. In univariate analyses, parental asthma and repeated wheezing at age the age of 0-1 years and 0-2 years predicted adulthood asthma. Repeated wheezing at age the age of 0-1 years predicted later bronchial reactivity. Onset and recurrence of wheezing at < 1 year of age, parental atopy and asthma, and maternal smoking during infancy were related to subnormal lung function parameters. In multivariate logistic regression, adjusted for sex, age on admission, current smoking, and atopy in infancy and, currently, repeated wheezing both at < 1 year and < 2 years of age was an independent predictor for adulthood asthma. Parental asthma and repeated wheezing predict adulthood asthma in infants hospitalized for bronchiolitis, and maternal smoking predisposes them to lung function impairment in adulthood.