Two hundred and twenty two children with persistent bilateral otitis media with effusion (OME) were treated with unilateral ventilation tube insertion and no treatment to the contralateral ear. The tympanic membrane changes in the operated and unoperated ears were compared during a 12 year follow-up. Segmental atrophy resulted from tube insertion whereas minor scarring and thickening of the pars tensa was related to the middle ear condition. Eight three percent of untreated ears and 85% of those treated with tubes did not develop atelectasis. Sixty percent of untreated ears and 64% of treated ears did not develop attic retraction. Very few cases (1.5 and 2%) in untreated and treated ears, respectively developed severe atelectasis. The overall duration of OME was assessed from the pre-operative history of hearing loss, the 3 month period of pre-operative observation and the post-operative time with effusion. There is a relationship between duration of the disease and development of both atelectasis and attic retraction.