400 patients with bilateral secretory otitis media (SOM) were treated with ventilating tubes (VT) in a prospectiv study. The ear drums were normal on both sides before VTs treatment thus allowing ear drum changes and complications during VT treatment to be recorded. 618 VT were placed in the ear drum after suction of the fluid. In 182 patients unilateral myringotomy with suction of fluid were done and VT placed in the contralateral ear. Adenoidectomy with myringotomy, with an obstructing adenoid, gave 30% better chance. 10 different VTs were used. The most frequent pathology found in the ear drum after one period of VT treatment was tympanosclerosis. In the ears only treated with myringotomy tympanosclerosis occurred in 1%. 3 factors seemed to give more tympanosclerosis: metal (stainless steel or titanium), polyethylene and prolonged stay-time in the ear drum. Chronic perforations of the ear drum occurred with great variations between the different tubes. The Goode modified T-tube caused perforations in 17%. In the other VTs the perforations occurred in 2.1%. Chronic perforation together with tympanosclerosis will happen more often when the VT is made of polyethylene compared to silicone or fluoroplastic (p < 05). 90% of the perforations were located at the site of the VT. The ideal VT will stay in for 8-18 months at an average and it can be shown to improve middle ear function better than only waiting or myringotomy. Long-term VTs should not be used at the first VT procedures.