Objectives: In recent years welfare in Denmark has increased which might be expected to reduce otitis media (OM) incidence. We examined the age-specific incidence of OM in a nation-wide cohort of children aged 0-7 years born in 1996-2003 (Danish National Birth Cohort, DNBC). Only selection was ability to understand and speak Danish. Methods: Information of OM and ventilation tubes (VT) was collected through three maternal interviews at 6-month, 18-month and 7-years of age and based on this age-specific and cumulative incidence of OM was calculated. As different numbers of the total population answered the different interviews, the calculations are done with different denominators. The information in DNBC was validated against two population based registries containing information of VT insertions. Results: Cumulative incidence of OM at 7 years was 60.6% (31,982/52,755). For children with OM, 16.2% (7143/44194) had their first OM episodes between 0-6 months of age, 44.3% (19579/44194) between 7-18 months, and 39.5% (17472/44194) between 19 months and 7 years. Four or more OM episodes before 7 years were reported by 39.5% (12620/31982) and by 64.0% (2482/3881) of those who had their OM debut between 0-6 months; by 48.2% (4998/10378) with debut between 7-18 months; and by 28.7% (4996/17344) with debut between 19 months and 7 years. These figures are essentially unchanged from earlier figures from Denmark. VT insertion at least once was reported by 26,1% in the 7-year interview. Assuming recordings in the Danish National Patient Registry to be gold standard, maternal self-reportings in DNBC of insertion of VTshowed high sensitivity (96.4%), specificity (98.2%), and positive (94.8%) and negative predictive values (98.8%). Conclusion: OM affects nearly 2/3 of preschool children in Denmark despite reduction in known OM risk factors.