Respiratory viruses are responsible for 10% of community-acquired pneumonia cases but do not cause nosocomial pneumonia. Herpesviridae, mainly herpes simplex virus and cytomegalovirus, are commonly detected in the respiratory tract of nonimmunocompromised, mechanically ventilated patients. Although their detection usually reflects viral reactivation without lung parenchymal involvement, in a particular subset of patients, viral lung disease (bronchopneumonitis) occurs. This bronchopneumonitis seems to have a true impact on outcome, but only interventional studies will be able to determine its real impact. Whether other viruses, such as mimivirus, are responsible for nosocomial pneumonia in mechanically ventilated patients requires additional studies.