The newly discovered human metapneumovirus (hMPV) has been shown to be associated with respiratory illness. We determined the frequencies and clinical features of hMPV and respiratory syncytial virus (RSV) infections in 374 Danish children with 383 episodes of acute respiratory tract infection (ARTI). Study material comprised routine nasopharyngeal aspirates obtained during 2 winter seasons (November-May) 1999-2000 and 2001-2002 from children hospitalized at the Departments of Paediatrics, Hvidovre Hospital and Amager Hospital, Denmark. hMPV was detected in 11 (2.9%) and RSV in 190 (49.6%) ARTI episodes by real-time reverse transcription-polymerase chain reaction using primers targeting the hMPV N gene and the RSV L gene. Two children were co-infected with hMPV and RSV. They were excluded from statistical analysis. Hospitalization for ARTI caused by hMPV was restricted to very young children 1-6 months of age. Asthmatic bronchitis was diagnosed in 66.7% of hMPV and 10.6% of RSV-infected children (p < 0.001). Overall symptoms and clinical findings were similar among hMPV and RSV positive episodes, but more RSV-infected children required respiratory support. hMPV is present in young Danish children hospitalized with ARTI although less frequent than RSV and with a tendency to a milder clinical course.