Respiratory syncytial virus (RSV) infects most people by the time they are 2 years old and reinfects throughout life. RSV is best recognised for causing bronchiolitis in infants--it is one of the most important respiratory pathogens in childhood in industrialised countries. The clinical manifestations of RSV infection in adults and elderly people, from upper respiratory tract infection to pneumonia, are less well known. Part of the burden of winter mortality in elderly people is attributable to RSV infection and it may be as important a cause of death as influenza. Recent advances in RSV vaccines have made RSV a more important topic for epidemiological research and surveillance. Basic research required before vaccine programmes can be developed includes describing the natural history of RSV infection in adults, quantifying the burden of disease attributable to RSV, and defining the best surveillance methods with which to evaluate different vaccination strategies.