We analyzed clinically 102 ears with secretory otitis media (SOM) belonging to 72 adult patients who during their adult life had not suffered previously from ear disease. As in children, most of the cases (63%) could be traced directly to an upper respiratory tract infection. The most striking finding was the preponderance of poorly pneumatized mastoids-which were measured planimetrically-among our SOM cohort. This was found in adult SOM ears compared to contralateral healthy ears (4.59 versus 7.88 cm2), as well as when all 102 SOM ears were compared with values of the normal population (5.41 versus 12.9 cm2). This study showed that poorly pneumatized mastoids are a significant risk factor as far as adult SOM is concerned.