Viral pneumonitides are among the known pulmonary complications of human immunodeficiency virus (HIV) infection. Cytomegalovirus (CMV) pneumonitis is the most frequently recognized viral infection involving the lung. Although CMV may occasionally be the sole pathogen found to be responsible for severe pneumonitis in patients with the acquired immunodeficiency syndrome (AIDS), in most cases, its role in causing pulmonary disease is less clear, primarily because of the propensity to infect with a variety of other copathogens. CMV pneumonitis has been difficult to diagnose during life, although techniques utilizing in situ DNA hybridization or monoclonal antibodies for detection of the virus may improve the diagnostic yield of less invasive procedures such as bronchoalveolar lavage. Pneumonitis due to herpes simplex virus, varicella-zoster, and respiratory syncytial virus have occasionally been reported in AIDS patients, and are of practical importance because of the availability of effective treatment. The role of influenza and adenoviruses in causing HIV-related pulmonary complications is unknown, but could be of importance during outbreaks of these infections. Finally, data from several studies now suggest that Epstein-Barr virus or HIV itself or both have a role in the pneumonitis. Further study in this area could provide information leading to more effective management of this common complication of childhood AIDS.