• Viral infections of the respiratory tract in infants and children are common. Little has been reported on roentgenographic findings associated with infection caused by common viruses other than with respiratory syncytial virus. We studied chest roentgenograms from 128 previously healthy infants and children who were infected with respiratory syncytial virus, parainfluenza virus, influenza virus, or adenovirus. Four common roentgenographic findings were detected: parahilar peribronchial infiltrates, hyperexpansion, segmental or lobar atelectasis, and hilar adenopathy. Diffuse interstitial infiltrates and significant pleural fluid accumulations rarely occurred in our series. We confirmed the popular but not well-documented belief that other common respiratory viruses can be associated with roentgenographic findings similar to those caused by respiratory syncytial virus. However, respiratory syncytial virus infection is associated with more abnormal chest roentgenograms than any of the other viruses regardless of the clinical syndrome. Hilar adenopathy was more common in adenovirus infection. Young infants had significantly more abnormal chest roentgenograms, with more hyperexpansion and parahilar peribronchial infiltration than older children. We also found a significant correlation between lobar atelectasis and severity of the illness. In infants and children with viral infection of the lower respiratory tract, roentgenographic information can be a useful adjunct to clinical viral diagnosis.