Recent advance in otologic surgical techniques, involving the use of an operation microscope, have led increased demands in accurate raiological diagnosis of the temporal bone. However, the difficulties of roentgen diagnosis of cholesteatoma of the middle ear are frequently experienced. Authors reviewed a total of 248 cases of mastoid roentgenograms(165 cases of cholosteatoma and 83 cases of chroni otitis media without cholesteatoma) surgically proven at Seoul National University Hospital from March 1977 to June 1980 in order that diagnostic value of routine mastoid roentgenogram (Towne and Law views) could be determined. The results are as follows ; 1. Detection rate of cholesteatoma is 68.5% with Towne view only and 62.4% with Law view only, while both Towne and Law views, it is increased up to 73.9%. 2. False positive is 10.8% even with both Towne and Law views. 3. A new simple technique, transorbital magnification view, introduced to visualize the detailed anatomic structu es of the ear.