The comparative association of respiratory syncytial virus group A and B infections with acute otitis media was determined by analysing the hospital records of children with community-acquired respiratory syncytial virus infection during three successive outbreaks from 1987 to 1992. Of 326 episodes analysed, 192 (59%) were caused by group A and 134 (41%) by group B infections. Acute otitis media was diagnosed in 101 (75%) children with group B infection, compared with 119 (62%) with group A infection (p = 0.01). Group A infections were more often associated with wheezing (71% versus 59% in group B; p = 0.02) and oxygen therapy in inpatients (48% versus 31%, respectively; p = 0.008). The higher incidence of acute otitis media associated with group B infections was observed both after adjustment for potential confounding variables and during each outbreak.