Background/Purpose: Human metapneumovirus (hMPV) is a newly discovered respiratory pathogen. This prospective hospital- based study investigated the clinical role and features of hMPV in Taiwan. Methods: Respiratory specimens collected from hospitalized children with acute respiratory tract infection between September 1, 2003 and April 10, 2005 were screened for metapneumovirus using real-time reverse transcription-polymerase chain reaction (RT-PCR). Results: During the study period, 930 specimens were obtained from 926 hospitalized children. After exclusion of 200 cases due to lack of clinical evidence of airway infection or diseases with known etiology, 726 were included in the analysis. Among these, 33 children had a positive result for hMPV infection. The majority of these patients were admitted during spring and early summer. Twenty-one (63.6%) were younger than 2 years of age. hMPV accounted for 13.3% of respiratory infections occurring between the ages of 18 and 24 months and was as common a respiratory pathogen as respiratory syncytial virus (RSV) in that age group. The 11 patients (33.3%) with underlying diseases had a similar disease course to those without underlying diseases. A co- pathogen was found in 11 patients (33.3%). Infected children between 2 and 5 years of age had significantly higher titers of hMPV in their respiratory specimens (10(3.88) copies/mu L) than children younger than 2 years (10(2.26) copies/mu L) (p = 0.013) and children older than 5 years (10 (2.25) copies /mu L) (p=0.005). hMPV positive cases were significantly older than those with RSV infection (p = 0.002 ) and had a shorter duration of hospitalization (p = 0.001), fewer days of oxygen use (p = 0.001) and higher levels of C -reactive protein (p = 0.004). Conclusion: Metapneurnovirus circulates in children in northern Taiwan during spring and early summer. hMPV was the most common respiratory pathogen in children aged between 18 and 24 months hospitalized with acute respiratory tract infection. Real-time RT-PCR is a sensitive method for investigating the epidemiology and diseases associated with hMPV. ; 附設醫院小兒部 ; 醫學院附設醫院 ; 期刊論文