Computed Tomography(CT) has been proved to be the most effective for detecting the bony erosion associated with cholesteatoma in chronic otitis media. Authors have studied retrospectively 20 cases diagnosed as chronic otitis media with cholesteatoma by operation with preoperative temporal bone CT and operative findings at the department of Otolaryngology of Ewha Womans University Hospital during the past three years from Jan. 1989 to Dec. 1991. The following results were obtained. 1) The range of age was 6 years to 40 years, and the highest frequency was the 3rd decade(11 cases) there was no difference in sex distribution. 2) The signs and symptoms of studied patients were hearing loss in 14 cases, otorrhea in 12 cases, headache in 3 cases, tinnitus in 2 cases, dizziness in 1 case and otalgia in 1 case. 3) The cholesteatoma was detected in the middle ear cavity in 9 cases and in the mastoid antrum in 13 cases by CT, but 10 cases and 17 cases each other by operative findings. The diagnostic predictability was 85.0% in middle ear cavity and mastoid antrum. 4) Erosion of malleus was seen in 3 cases, incus in 5 cases, stapes in 1 case and ossicular absence in 1 case by CT, but erosion of malleus in 6 cases, incus in 10 cases, stapes in 2 cases and ossicular absence in 3 cases were seen by operative findings. The diagnostic predictability was 75.0%, 65.0%, 85.0%, 90.0% in each status. 5) The state of drum was detected as perforation in 7 cases, adhesion in 1 case and retraction in 6 cases by CT, but perforation in 14 cases, adhesion in 2 cases and retraction in 1 case by operative findings. The diagnostic predictability was 55.0% in perforation, 95.0% in adhesion and 75.0% in retraction. 6) The destruction of surrounding bony structure was observed in lateral attic wall in 6 cases and in posterior bony wall in 1 case by operative findings. The narrowing of the external auditory canal was seen in 2 cases by CT and operative findings. 7) The erosion of the facial canal was detected in tympanic segment in 2 cases and in mastoid segment in 1 case by CT. 8) The dural plate bony dehiscence was detected in 2 cases by operative findings, but not detected by CT.