Ninety ears (52 patients, aged 3-11 years) affected by secretory otitis media (SOM) were treated by insertion of a ventilation tube (VT). Following VT insertion, the middle ear air volume of these ears was estimated by using an impedance audiometer, at 1, 3, and 6 months postoperatively, and every 6 months thereafter. The middle ear air volume, expressed as the compliance value, increased rapidly for the first 3 months, followed by a gradual increase thereafter. A great difference was observed among the compliance values of ears, ranging from over 10 cc to below 1.5 cc at 6 months, postoperatively. Twelve percent of the ears had compliance values of less than 1.5 cc, and in this group, CT showed opacified and poorly developed mastoid cells. Although the association of upper respiratory disorders such as chronic sinusitis, nasal allergies and cleft palate were found to be more frequent in cases of ears with smaller compliance values, this was not statistically significant. Small compliance values (middle ear air volume) were correlated with the early onset of acute or secretory otitis media, repeated otorrhea after VT insertion and high recurrence rates after the extrusion of the VT.