Eighty-nine cases of attic type cholesteatoma were operated on during a three and a half-year period. Of these, eight cases were characterized by bony tissue proliferation at the aditus ad antrum or mastoid antrum. Sex, age, and hearing levels were not significant in these cases. Bony fixation of the incus and the malleus was seen in six cases. Bony tissue blocked further expansion of attic cholesteatoma at the aditus in four cases, narrowed the epithelial tract to the antrum in two cases, and completely separated the cholesteatoma into two cholesteatomas in two cases. Infectious stimuli, at an early stage of the disease, might stimulate such osteoplastic activity at the aditus. Axial CT scans give useful information regarding structure before surgery.