ObjectiveOtitis media is a disease that commonly occurs in infants. Various risk factors have been reported. Sleep position has been reported to be associated with various diseases. There is no report on the relationship between otitis media and sleep position. We examined the incidence of otitis media and sleep position in infants. MethodsWe used data from the Japan Environment Children's Study. We used multivariate logistic analysis to examine the relationship between sleep position and the incidence of otitis media in infants aged up to 6 months. In addition, we conducted a stratified analysis based on whether the child was able to turn over in bed at 6 months of age. ResultsThe study population comprised 85,731 participants. The incidence of otitis media by sleep position was significantly higher when the infant was in the prone position compared to any other position (adjusted odds ratio, 1.206; 95 %CI, 1.038–1.401). Stratified analysis of turning showed that otitis media was more common in the prone position in all groups. ConclusionIn the current study, infants aged 6 months or younger who slept in the prone position were more likely to have otitis media. Sleep position interview and guidance on changing sleep position may be useful for the prevention of otitis media.