Using sectional images of high resolution computed tomography, a quantitative analysis of bone destruction has been undertaken in 73 adult cases with cholesteatoma, 52 having a pars flaccida cholesteatoma (PFC) and 21, a pars tensa cholesteatoma (PTC). These cholesteatomas were further classified into two subtypes: an extended type (cholesteatomas that had extended into the antrum) and a non-extended type (cholesteatomas without an antral extension). Similarly analyzed were 60 cases manifesting chronic otitis media with a central perforation (COM) comparatively. This analysis was performed by means of two-dimensional images and by linear measurement, taken at specific locations in each middle ear cavity. The results revealed that the width of the attic was significantly greater in both the PFC and PTC cases than in the COM cases. Further, a significantly greater distance between the malleus and the lateral wall of the attic was seen in the PFC cases than in the COM cases. In contrast, the distance between the malleus and the medial wall of the attic was significantly greater in the PTC cases than in the COM cases. The extended-type cases had significantly greater distances than did the COM cases with regard to the width of the aditus ad antrum, and the width and anterior-posterior diameter of the antrum. These distances, however, did not significantly differ between the non-extended-type cases and the COM cases. It thus appears that these distances, caused by bone destruction, appear to parallel the extension of the cholesteatoma into the antrum.