BACKGROUND: We have described occurrence and clinical manifestations of human coronaviruses (HCoV) in hospitalized Norwegian children with respiratory tract infection (RTI) and compared them with a group of respiratory syncytial virus (RSV)-infected children. METHODS AND POPULATION: We used in-house TaqMan multiplex real-time polymerase chain reaction to test nasopharyngeal samples from 536 RTI episodes in 452 children who were admitted during the 2006-2007 winter. Twenty-one viruses, including HCoV-OC43, HCoV-NL63, HCoV-229E, HCoV-HKU1, and RSV were tested. The amount of viral nucleic acid was recorded semiquantitatively based on the cycle threshold value. RESULTS: A total of 665 positive polymerase chain reaction tests were recorded in 536 nasopharyngeal specimens. Coronavirus was found in 68 (12.7%): HCoV-OC43, n = 44 (8.2%), and HCoV-NL63, n = 24 (4.5%). Only RSV and rhinovirus were detected more frequently. Neither HCoV-229E nor HCoV-HKU1 was detected. Among children with HCoV-OC43, 73.0% tested positive for at least one other virus, compared with 41.2% with HCoV-NL63 and 40.3% with RSV (P = 0.03 and P < 0.01, respectively). Children with HCoV-OC43 and HCoV-NL63 were older than children with RSV (median age, 19 vs. 10 months, P = 0.01). Lower respiratory tract infection (LRTI) was half as common in children with HCoV-OC43 (48.6%) and HCoV-NL63 (47.1%) as in children with RSV (82.3%) (both P < 0.01). After adjusting for age, chronic disease, LRTI, and co-detection of other viruses in a multiple logistic regression analysis, HCoV was associated with a shorter fever period and shorter hospitalization time than RSV. CONCLUSIONS: HCoV-OC43 and HCoV-NL63 are common among hospitalized Norwegian children with RTI. Children with HCoV-OC43 and HCoV-NL63 have LRTI less frequently and may need a shorter hospital stay than children with RSV.