Impedance audiometry was performed as a part of the routine preoperative examination in a consecutive series of 162 children with no hearing problems who underwent adenotonsillectomy. The complete impedance battery was of great diagnostic value for OME (Otitis media with effusion) and we were able to detect OME in 30 children (18.5%). The data on the distribution of the various measures of impedance audiometry indicated that younger children with adenotonsillectomy had higher incidence of abnormal tympanogram (type B or C): 26.2% in 4-6 year old, 22.6% in 7-9 year old, 12.8% in 10-13 year old respectively. There was no significant difference in the static compliance between the adenotonsillectomy group without OME and the control. The mean acoustic reflex threshold for 7-13 year old children with adenotonsillectomy showed higher level, ranging from 107 dB to 109 dB, than normal acoustic reflex threshold, suggesting an evidence of undetected middle ear disorders.