Cholesteatomas are thought to result from ingrowth of keratinizing squamous epithelium from external ear tomiddle ear. The Cholesteatomas are usually diagnosed by clinical symptoms and signs, otoscopy, and plainradiograms. But various view points are emphasized radiologically before operation, leading to examine by CT, especially in complicated cases. We retrospectively reviewed the CT findings of cholesteatomas in 25 surgicallyproven cases during the period from May, 1983 to Aug, 1988. The results were as follows: 1. Most cholesteatomas showed soft tissue mass and bony erosion of ossicles (88%), attic wall and mastoid antrum (84%) on temporal bone CT scan. 2. The CT numbers of cholesteatomas ranged from 25 to 50HU(avg.33HU). 3. Involved sites were attic(16%),antrum(28%), and both attic and antrum(56%). Other sites were middle ear cavity and external auditory canal. 4.Extra-tympanomastoid extension of cholesteatoma was intracranial abscess(8%), exposure of dural sinus(8%), and extension along with neck(4%).