The present study was aimed to investigate characteristics of lower respiratory tract infections caused by parainfluenza type 3 viruses. Nasopharyngeal smears were taken from 178 patients with lower respiratory infections for the diagnosis of respiratory syncytial virus, adenovirus, influenza and parainfluenza viruses between December 2004 and April 2005. Parainfluenza type 3 was isolated from the viral specimens of 96 (53.9%) patients and it was noticeable that the parainfluenza type 3 outbreak occurs during winter. Obviously, improving the aetiological diagnosis of viral infections might avoid unnecessary therapy, antibiotics in particular, and would allow for preventive isolation of infected patients.