By performing annual tympanometric screenings of randomly selected children in the winter, the changes in the point prevalence rate of secretory otitis could be estimated during childhood. The tympanometric conditions deteriorated from the age of 4 to the age of 5, and a significant increase in the point prevalence of type B, i.e. flat curve, from 14 to 18% was noted. However, from the age of 5 to the age of 6, an insignificant change was found in the point prevalence of type B (15%) and Eustachian tube dysfunction. In contrast, a marked improvement of the function of the Eustachian tube as well as a drastic fall in the prevalence of secretory otitis to 7 % could be demonstrated from the age of 6 to the age of 7. At each trial some children have dropped out for various reasons. However, the tympanometric conditions of the dropouts largely followed the general pattern of the children who attended all trials.