Introduction Otitis media is the primary cause of antibiotic prescription in children. Two-thirds of all children experience at least one episode of otitis media before the age of 7 years. The aim of this study was to characterise the attributable effect of several modifiable risk exposures on the risk of >3 episodes of otitis media at age 18 months and 7 years within a large prospective national birth cohort. Methods The study used the Danish National Birth Cohort comprising information about otitis media and risk exposures from more than 50,000 mother-child pairs from the period 1996–2002. Logistic regression models were used to estimate odds ratios for the risk factors and to calculate the population attributable fraction. Results Short time with breastfeeding, early introduction to daycare, cesarean section, and low compliance to the national vaccination program were all associated with an increased risk of >3 episodes of otitis media at 18 months of age and at 7 years of age. The fraction of children with otitis media attributed from breastfeeding lasting for less than 6 months was 10%. Introduction to daycare before the age of 12 months attributed with 20% of the cases of >3 episodes of otitis media. Conclusions Short duration of breastfeeding, early introduction into daycare, cesarean section, and low compliance with the national vaccination program increased the risk of experiencing >3 episodes of otitis media at 18 months, and at 7 years of age. These are factors that all can be modulated.