Background Otitis media with effusion is a highly concurrent disease in young children with adenoid hypertrophy.The aim of this study was to assess the middle ear effusion and audiological characteristics in children with adenoid hypertrophy and compare the various assessment methods.Methods Two hundred and seven candidates who were to undergo adenoidectomy were analyzed using otoscopy,tympanometry,air-conduction auditory steady-state responses (AC-ASSR),and computerized tomography (CT) before adenoidectomy.Results About 73.4％ (304/414) of ears were confirmed to have middle ear effusion (MEE) by otoscopy; 75.4％ (312/414) of ears revealed MEE by CT.CT scan correctly predicted all the myringotomy results,giving 100％ accuracy on the diagnosis of MEE.Additionally,CT revealed two children with inner ear malformations.Type B tracing tympanogram provided a sensitivity of 91.7％ and a specificity of 92.2％.Type C tympanogram with peak pressure <-200 daPa indicated effusion; type C tympanogram having acoustic stapedius reflex could exclude MEE.We excluded the AC-ASSR results of the 4 ears with malformation; 54.4％ (223/410) of ears were confirmed of hearing loss.Furthermore,5.2％(16/310) of the ears with MEE suffered from severe to profound hearing loss.The average threshold level in the 0.25 kHz frequency of children was found to have poorer hearing thresholds than those in the 0.5,1,2,and 4 kHz (P <0.001) frequencies; 29.7％ (92/310) of ears with MEE were regarded as normal hearing level.About 55.8％ (173/310) of ears with MEE were classified as having slight-mild hearing loss.Conclusions The practitioners should pay much attention to the middle ear condition and be aware of a possible development of severe to profound hearing loss during the course of MEE in young children with adenoid hypertrophy.CT scan is good for the assessment of MEE before ventilation tube insertion.