A random sample of 2512 children were monitored to an average age of two years to determine the occurrence of acute otitis media (AOM). A life-table methodology was employed in the analysis. The cumulative incidence of the first episode of AOM up to 12 months of age was 42.4% (95% confidence interval 40.4-44.4) and the corresponding figure up to 24 months of age was 71.0% (68.9-73.1). The incidence rate for all acute otitis media episodes was 0.93 episodes per child per year (0.90-0.96) during the first 24 months of life increasing in the spring and autumn. The risk of experiencing an episode of acute otitis media increased at the age of 6-12 months and decreased slowly during the second year of life. The results confirm the frequent nature of acute otitis media and stress the necessity for clear, consistent definition of the criteria for acute otitis media in epidemiological research.