Revision surgery was performed in 66 ears with chronic otitis media which had earlier undergone tympanomastoid operation in Seoul National University Hospital. The indications for revision surgery were hearing loss in 71.2%, recurrent or residual cholesteatoma in 24.2% and others. The mean interval between the first and revision operation was 34.4 months. Canal down surgery had been made in 33 ears and canal wall up surgery in 33 ears. Cholesteatoma was found in 25.0% of previous cholesteatoma ears and 16.7% of previous non-cholesteatoma ears. Among the ears which had ossiculoplasties with autograft or homograft ossicles, strut was normal in 28.6%, dislocated in 35.7%, fixed in 26.2% and eroded or absent in 9.5%. All the struts were malpositioned in the ears which had been reconstructed by synthetic material. The result in terms of the improvement of average hearing levels for 0.5, one and two kHz was 6.85 dB as a mean value.