BACKGROUND: Parainfluenza virus (PIV) is a significant cause of acute respiratory infections. Epidemiological information on PIV infection could be very helpful for patient management. The aim of this study was to investigate the epidemiology of PIV infection in Seoul and a neighboring area with regard to PIV type. METHODS: The diagnosis of PIV infection was made by virus isolation. The R-mix Too cell system (Diagnostic Hybrids, Inc., Athens, OH, USA) and D3 Ultra DFA Respiratory Virus Screening & ID kits (Diagnostic Hybrids, Inc.) were used for virus culture and identification. The medical records of patients with positive virus cultures were reviewed retrospectively. RESULTS: Seven hundred and ten PIV viruses (5.6%) were isolated from 12,723 specimens. The number of subjects with PIV type III, I and II was 357, 304 and 49, respectively. PIV infection showed a peak incidence in the first year of life regardless of subtypes. The most common diagnosis among all PIV subtypes was pneumonia. Lower respiratory tract infections constituted the majority (76.3%) of PIV infections. The most common diagnosis of PIV type I and II was croup and that of PIV type III was pneumonia. A difference in seasonal variation between subtypes was observed. PIV I (62.2%) was mainly isolated from July to September while PIV type III (86.8%) was isolated from April to July. CONCLUSION: Lower respiratory infection was most commonly found in hospitalized patients with PIV infection. Clinical features of PIV infection were similar those seen in Western PIV reports, with the exception of the seasonal outbreak pattern.