OBJECTIVE: It is recognized that human rhinovirus (HRV) infection is an important factor in asthma exacerbations requiring hospitalization in children. However, previous studies have disagreed on the differential impact of various HRV species. We sought to assess the impact of HRV species on the severity of asthma exacerbations in children and adolescents. We also examined whether the effect of HRV species on severity was modified by age and gender. METHODS: Virus strain was determined for 113 children with HRV detectable at the time of admission for asthma exacerbation. Patient characteristics were collected on admission and exacerbation severity was scored using several validated scales. RESULTS: HRV species by itself was not associated with moderate/severe vs. mild exacerbations. Boys with HRV-C infections were more likely (OR: 3.7, 95% CI: 1.2-13.4) to have a moderate/severe exacerbation than girls with HRV-C (p = 0.04 for interaction term). Higher odds were observed in younger boys (3 years old: OR: 9.1, 95% CI: 1.8-47.1 vs 5 years old: OR: 3.3, 95% CI: 0.9-11.8 vs 7 years old: OR: 1.2, 95% CI: 0.2-6.6). In contrast, children with HRV-C infection and sensitized to pollen during the pollen season were less likely to have moderate/severe exacerbations (p = 0.01 for the interaction term). CONCLUSION: Acute asthma exacerbations are more likely to be moderate/severe in boys under 5 years of age who had HRV-C infection on admission. The opposite was found in children with sensitization to pollen during pollen season.