Screening tympanometries were performed at 2-week intervals in 373 children (mean age 4 1/4 years) cared for in 10 day-care centers in order to evaluate the incidence of secretory otitis media (SOM). The incidence was found to depend on the age of the children and the maximum level was at the age of 1 (0.36/child/month); the mean incidence was 0.16/child/month. The highest incidence and the largest number of children with prolonged SOM were both found in the 1-year-olds. The overall morbidity of SOM in the 373 children was 56%.