Otitis media with effusion (OME), is a frequent sequela of acute otitis media in young children, and pathological changes in the middle ear cavity are often silent. To better understand the pathogenesis of otitis media with effusion and the development of chronic middle ear sequelae, the epithelial histopathology of middle ear mucosa was studied in 85 temporal bones with middle ear effusion and in 29 normal temporal bones from children younger than 10 years of age, using a semiquantitative method. Morphometric analysis was done in specimens with serous, purulent, and mucoid effusions with or without chronic pathologic tissue such as granulation tissue. The incidence of granulation tissue in the middle ear cavity was higher in mucoid effusion than in serous or purulent effusion. The density of ciliated and goblet cells differed in various types of middle ear effusion and in the presence or absence of granulation tissue. The density of ciliated and goblet cells was greatest in mucoid effusion with or without granulation tissue. These findings suggest that both the epithelium and subepithelium of middle ear mucosa may play an important role in the pathogenesis of otitis media with effusion. These results indicate that the middle ear histopathology in mucoid otitis media often reaches the stage of chronic changes silently. Since mucoid otitis media is the most common type of chronic otitis media with effusion in young children, these findings have considerable clinical relevance and call attention to the importance of early intervention to prevent serious chronic changes in ears with otitis media with effusion.