['Human rhinoviruses (HRV) are now considered major respiratory pathogens. We sought to determine whether HRV are a cause of wheezing and/or hospitalization in children <2 years old.', 'A polymerase chain reaction assay was used to screen for HRV infection in 4 categories of children <2 years old: (1) with symptoms of respiratory tract disease without wheezing; (2) with wheezing with or without other symptoms; (3) who were asymptomatic and; (4) who had a respiratory specimen submitted to a diagnostic laboratory. All specimens were collected between January and December 2004. Phylogenetic analyses were performed on most HRV isolates.', 'Twenty-eight (17%) of 165 children with symptoms of respiratory infection without wheezing; 21 (26.3%) of 80 children with wheezing; 3 (3%) of 93 asymptomatic children; and 47 (23.3%) of 202 children with specimens submitted to the diagnostic laboratory tested positive for HRV. The difference between the rates of infection in the asymptomatic group and in each of the 3 other categories was statistically significant (P </= 0.01). Among HRV-positive children with samples submitted to the diagnostic laboratory, 55% were hospitalized, which was similar to that observed for respiratory syncytial virus (52.7%) among children of a similar age group and time period (P = 0.85). Diverse groups of HRV were circulating during the 1-year study period.'] Are rhinoviruses a major cause of wheezing and hospitalization in children less than 2 years of age?