Respiratory syncytial virus (RSV) causes pneumonia and bronchiolitis in infants and young children and serious disease in the elderly and persons with compromised immune systems. To determine the temporal and geographic patterns of RSV outbreaks in the United States, monthly reports from 74 laboratories were analyzed for July 1985 through June 1990. RSV outbreaks were identified in 197 (93%) of the 211 laboratory years analyzed, with widespread activity beginning each fall, peaking in winter, and returning to baseline in April or May. Each year, the timing of outbreaks did not differ significantly between most regions; the few differences were small, and no region consistently had early or late outbreaks. These findings are consistent with RSV transmission within communities rather than between communities or regions. Health care personnel should consider the possibility of RSV infection in their treatment and prevention efforts from November through April each year in the United States.