Respiratory infections are frequently encountered in the community; these infections are usually associated with only minor consequences. Many different agents, such as influenza and parainfluenza virus, respiratory syncitial virus, rhinovirus, coronavirus, adenovirus and herpes virus can be found in immuno-competent patients. Among these pathogens, cytomegalovirus (CMV) has been found to be responsible for nosocomial pneumonia in ICU. The main problem for viral infections, is the diagnosis, isolation of the pathogen is often difficult and not always reliable and the symptoms not specific. However, influenza is characterised by fever, myalgia, headache and pharyngitis, this infection may be very mild, even asymptomatic, moderate or very severe. Finally, the most recent viral pathogen involved in respiratory disease is a newly discovered coronavirus, the SARS-CoV which was responsible for the worldwide outbreak of Severe Acute Respiratory Syndrome. Viral pneumonia is a common pathology which is probably underdiagnosed in immuno-competent patients; many reports show that even if the diagnosis is difficult to obtain, it is not useless as long as we have, for most of the pathogens, an effective treatment. The gold standard was histology, new techniques like PCR can probably make a difference and should be included in the guidelines to improve diagnostic efficiency.