Background: Mucins function in the normal physiology of the middle ear and in the pathophysiology of otitis media with effusion (OME). The adenoid is felt to play a role in otitis by serving as a bacterial reservoir and propagating the inflammatory state of the middle ear. We wished to determine the MUC 5AC mucin gene expression in the adenoids of children with and without OME. Methods: Adenoid specimens were collected from children with and without OME (n=14) and MUC 5AC expression quantitated using RT-PCR. Results: This demonstrated a normalized value of 44.8 au±53.8 for MUC 5AC in children with OME and 159.8 au±97.2 for MUC 5AC in children without OME (p=0.02). Conclusions: Although mucin accumulation in the middle ear causes morbidity (hearing loss) in children, our results suggest there is less MUC 5AC expression in the adenoids of children with OME as compared to those without OME. These results emphasize the role of mucin in normal physiology and host defense, and may implicate defects in mucociliary transport, Eustachian tube function, or quality of mucin rather than quantity of mucin produced in the pathophysiology of otitis media.