We previously reported an increased risk for bronchial obstructive disease and allergic sensitization up to age 3 in 47 children hospitalized with a respiratory syncytial virus (RSV) bronchiolitis in infancy compared with 93 matched control subjects recruited during infancy. The aims of the present study were to evaluate the occurrences of bronchial obstructive disease and allergic sensitization in these children at age 7(1)/ (2). All 140 children reported for the follow-up, which included physical examination, skin prick tests, and serum IgE tests for common food and inhaled allergens. The cumulative prevalence of asthma was 30% in the RSV group and 3% in the control group (p < 0.001), and the cumulative prevalence of "any wheezing" was 68% and 34%, respectively (p < 0.001). Asthma during the year prior to follow-up was seen in 23% of the RSV children and 2% in the control subjects (p < 0.001). Allergic sensitization was found in 41% of the RSV children and 22% of the control subjects (p = 0.039). Multivariate evaluation of possible risk factors for asthma and sensitization using a stepwise logistic statistical procedure for all 140 children showed that RSV bronchiolitis had the highest independent risk ratio for asthma (OR: 12.7, 95% CI 3.4 to 47.1) and a significantly elevated independent risk ratio for allergic sensitization (OR: 2.4, 95% CI 1.1 to 5.5). In conclusion, RSV bronchiolitis in infancy severe enough to cause hospitalization was highly associatied with the development of asthma and allergic sensitization up to age 7(1)/ (2). The results support the theory that the RSV influences the mechanisms involved in the development of asthma and allergy in children.