This study investigated the usefulness of three-dimensional computed tomography (3DCT) in the evaluation of bony defects caused by cholesteatoma. Fifteen patients with chronic otitis media with cholesteatoma who showed bony destruction or suspicious destruction in two-dimensional CT were examined using 3DCT. The CT data were transferred to a workstation witha real-time image processor. We used three-dimensional reconstruction software enabling image processing. In all patients, 3DCT clearly delineated the destruction of bony structures by cholesteatoma. The 3DCT-generated images provided spatial relationships, which were not easily appreciated on two-dimensional CT. Intraoperative bony destruction findings correlated with 3DCT findings. From these results, 3DCT could be useful to evaluate the invasiveness of cholesteatoma to the cranial base. It could also be helpful in planning reconstruction during surgery.