ySummary Objective: Adenoidectomy is being generally used for the treatment of otitis media with effusion (OME). The purpose of current study was to determine objectively the significance of the histopathology of adenoid tissue on the development of otitis media with effusion. Methods: The records of all the patients operated on with the diagnosis of adenoid enlargement with or without OME were reviewed and pathologic specimen were re-evaluated regarding histopathological properties by one pathologist unfamiliar with the diagnosis. Sixty-one patients with adenoid hyperplasia, were enrolled in the study group, 38 mates and 23 females. Age ranged between 3 and 13 years (mean age was 7.03 +/- 3.26 years). All the patients of study group were those operated on due to the adenoid hyperplasia and uni- or bilateral OME. Control group was composed of 39 mate and 26 female patients (age range was between 3 and 13 years, and mean age was 7.06 +/- 3.04 years) with solely adenoid hyperplasia. Results: The squamous metaplasia was present in 47 (77%) and 14 (22%) patients of study and control groups, respectively. The fibrosis of connective tissue interspersed follicles of adenoid was present in 29 (48%) and 6 (9%) patients of study and control groups, respectively. The statistical analysis revealed a significant prevalence of squamous metaplasia (P < 0.001) and fibrosis of connective tissue interspersed follicles of adenoid (P < 0.001) for a surgical indication of adenoid hyperplasia with OME than for without OME. The prevalence of other parameters was not significantly different between two groups. Conclusions: Adenoid tissue not only exerts an obstructive influence on the eustachian tube lumen when enlarged, but also impedes (hinders) mucociliary drainage of the middle ear by the way of non-ciliated metaplastic epithelium and fibrosis of connective tissue. (C) 2003 Elsevier Ireland Ltd. All rights reserved.