Characterization of the etiology of severe pneumonia according to demographic and clinical characteristics is essential for proper management and prevention. Adenovirus has been reported as a common cause of severe community-acquired pneumonia (CAP) in young, healthy military trainees. With the availability of polymerase chain reaction, respiratory viruses are increasingly recognized as important causes of severe CAP in adults. Further efforts should be given to investigation of the clinical impact of viral pneumonia and the role of antiviral therapy.