Objectives: Concordance between sinusitis and otitis media with effusion (OME) has been reported in 5-60% of patients. Since nasal diseases induce edema and lymphoid tissue hyperplasia in the nasopharyngeal mucosa, especially the adenoids, chronic infection of the adenoids has been reported to induce otitis media. In addition, deterioration in the mucosal barrier of the adenoids makes the latter vulnerable to bacterial. infections, resulting in OME or sinusitis. We therefore evaluated adenoid local immunity and Eustachian tube function by sinusitis and the concordance between sinusitis and OME. Materials and methods: We examined PNS series and tympanometry of 520 patients who had undergone adenotonsillectomies. In addition, local adenoidal immunity was evaluated in 10 children with OME and sinusitis, 11 with only sinusitis, 10 with only OME and 12 with no history of OME or sinusitis. Adenoid size, squamous metaplasia, IgA, BCL-6, and mucosal barrier were also determined. Results: Of 520 patients, 80 (15.4%) had both OME and sinusitis. The incidence of Eustachian tube dysfunction differed significantly between patients with and without sinusitis (p = 0.03). The incidence of squamous metaplasia differed significantly between patients with sinusitis plus OME and patients with sinusitis atone (p = 0.01), and between patients with OME atone and those without both conditions (p = 0.005). Patients with both sinusitis and OME differed significantly in IgA secretion (p = 0.01) and Bcl-6 expression (p = 0.02) from those with sinusitis alone, as did patients with OME atone and those without both conditions (p = 0.02 and p = 0.03, respectively). Conclusions: Sinusitis plus OME were present in 15.4% of patients. Eustachian tube dysfunction was present in 37.9% of sinusitis patients and in 28.4% of those without sinusitis. IgA, BCL-6 and squamous metaplasia were important in local adenoidal immunity. (C) 2008 Elsevier Ireland Ltd. All rights reserved.