Most recent epidemiologic studies identify breast feeding as a significant protective factor for the development of otitis media. However, the magnitude of its potential effects with respect to actue otitis media (AOM) and chronic otitis media with effusion (OME) warrants further research. We followed consecutively enrolled infants from shortly after birth until 24 months of age. Peak incidence occurred between 8 and 12 months of age. Infants exclusively formula fed for the first 3 months of life demonstrated a marginally elevated risk of middle ear disease compared to infants exclusively breast milk fed (RR=1.22, 95% CI:.97-1.54). The nearly 30% elevated risk(RR=1.28, 95% CI:1.03-1.59) shown for exclusively formula fed infants at 6 months suggests (immunologic) protection may be imparted with duration of breast feeding. Infants who were formula fed during the first 6 months had a 40% elevated risk of a first episode of AOM but not OME occurring in infancy. Additionally, formula feeding did not appear to be related to elevated risk of recurrent episodes of AOM or OME. This finding implies that the putative benefit of breast milk observed in this infant cohort provides little protection against re-infection.