The human metapneumovirus (hMPV) was recently identified and linked to acute respiratory tract infections (ARTI). To assess the clinical importance of this virus in infants and children, we developed a rapid and efficient reverse transcription-PCR-based screening method for a large volume of samples and tested retrospectively a collection of 1,132 respiratory specimens submitted over a full year period to the virology laboratory of a large tertiary care pediatric center in Montreal, Canada. A total of 41 samples from 37 patients were positive by this method. During the winter months of 2001, up to 8% of specimens submitted for respiratory virus testing were hMPV positive. Sequencing data of the hMPV M gene revealed that two genogroups of the virus, each of which can be divided into two subgroups, cocirculated during this time period. A case-controlled study was conducted to compare the symptoms associated with hMPV infection with those involving other etiologic agents causing ARTI. Symptoms most frequently observed in hMPV-positive patients were cough, wheezing, and dyspnea, although the symptomatology could differ substantially from patient to patient. No distinct symptom profile could be associated with hMPV. Three nosocomial cases of hMPV infection were identified. Together, our data suggest that hMPV is a significant cause of symptomatic respiratory tract infections in infants and children. The incidence of the disease and the morbidity associated with the infection justify adding hMPV to the list of common respiratory viruses routinely screened for by clinical laboratories.