The cholesteatoma is usually associated with chronic purulent otitis media and destroys the surrounding structures and may cause dangerous complications. Once a cholesteatoma is present, surgical procedure such as radical or modified radical mastoidectomy should be considered. The X-ray diagnosis should by attempted in every cholesteatoma case before operation, but even more frequently, a cholesteatoma is found during operation in spite of negative X-ray findings. According to the reports of each authors, the diagnotic rate of a cholesteatoma by the simple mastoid X-ray could be made in only about one third of cases by Mygind (1932), in about 40% by Winderen and Zimmer (1954), and in about 60% by Bruner et al (1966). By the clinical study of the cholesteatoma in diagnosis by the simple mastoid X-ray, our results are as followed : 1) The 62 cases (30.5%) were confirmed to cholesteatoma by the ear surgery, among the 203 cases of all ear surgery. 2) We could detected the 23 cases (37.1%) preoperatively by the simple mastoid X-ray, among the 62 cases of cholesteatoma. 3) We could not found apparent difference in sex ratio (33 : 29 in male to female) and the most common age group was between 30 and 39 years included 19 cases (30.6%), among the 62 cases of cholesteatoma. 4) The most common site of a cholestestoma in surgery was attic and included the 29 cases (46.8%) among the 62 cases. 5) The most common site of a cholesteatoma by the simple mastoid X-ray was attic and mastoid antrum, and included the 15 cases (65.2%), among the 23 cases of cholesteatoma which were detected by the simple mastoid X-ray. 6) We could found the bone erosion in the attic, antrum or both in surgery, and the 18 cases (78.3%) were included among the 23 cases. 7) The most common site of bone erosion on the simple mastoid X-ray was attic and mastoid antrum, and the 12 cases (66.7%) were included among the 18 cases. 8) We could not found the bone erosion in surgery in the 33 cases (84.6%) of cholesteatoma, among the 39 cases which revealed the negative findings of cholesteatoma on the simple mastoid X-ray. 9) The most common site of cholesteatoma which revealed the negative finding on the simple mastoid X-ray was attic and the 26 cases (66.7%) were included among the 39 cases.