Our aim was to obtain knowledge of how meteorological conditions affect community epidemics of respiratory syncytial virus (RSV) infection. We recorded year-round RSV activity in nine cities that differ markedly in geographic location and climate. We correlated local weather conditions with weekly or monthly RSV cases, and reviewed similar reports from other areas varying in climate. Community activity of RSV is substantial when both ambient temperatures and absolute humidity are very high, perhaps reflecting greater stability of RSV in aerosols. Transmission of RSV in cooler climates is inversely related to temperature. UVB radiation may inactivate the virus in the environment, or influence susceptibility to RSV by altering host resistance. Activity of RSV in the community is controlled by many factors, including climate and behaviour of the population. Accurate information on when to institute and withdraw prophylactic therapy against RSV will depend on local epidemiological data.