150 children aged between 2 and 9 years (mean 5.25 years) with chronic bilateral otitis media with effusion were randomly allocated to three groups who, in addition to unilateral myringotomy and grommet insertion, would have an adenotonsillectomy, an adenoidectomy, or neither. The contralateral ear was assessed. Otoscopic, impedance, and audiometric findings were recorded preoperatively and at six and twelve months postoperatively. Subtraction of the no-surgery results indicates that at twelve months adenoidectomy produces otoscopic resolution of OME in 41.7% and no-peak/peak conversion of impedance in 29.8%. The hearing gain from adenoidectomy alone was similar to that resulting from insertion of a grommet alone, but the children having adenoidectomy required fewer reinsertions to maintain adequate subjective hearing thresholds in the treated ear (26% versus 54%). Tonsillectomy conferred no additional benefit. Without treatment there was a small but significant improvement in all indices at twelve months but not at six months postoperatively.