Respiratory Syncytial Virus, generally recognized for its role as the major respiratory pathogen in newborn infants and young children, is also a significant pathogen in adults. It is a frequent cause of upper and lower respiratory illness among all age groups, although it often goes unrecognized in adults unless highly sensitive molecular diagnostic tests are used. All RSV infections in adults represent re-infection and are generally mild to moderate in severity, although persons with certain high-risk conditions are susceptible to severe disease. These include the frail elderly living at home or in long term care facilities, those with underlying chronic pulmonary disease, and the severely immunocompromised. It is estimated that between 11,000-17,000 adults die of RSV infection annually in the U.S, with ~ ten-fold more admitted to hospital with respiratory symptoms. As in infants, wheezing is often noted during RSV infections and chest radiographs are often normal despite significant lower respiratory symptoms and hypoxia. Treatment of RSV is directed at symptomatic relief, and only rarely is specific antiviral therapy recommended. Exceptions include the severely immunocompromised, in whom inhaled ribavirin has been recommended in hopes of reducing both mortality and long term pulmonary compromise, especially in lung transplant recipients. Immunity to RSV is incomplete. Although there does not appear to be a defect in humoral immunity, there is evidence that CD8+ T cell immunity may be impaired with age. Currently a vaccine for RSV is not available, and many challenges to developing a successful vaccine must be overcome.