The authors present their experience of secondary cholesteatomas of the middle ear explored by computerized tomography (CT). Following a brief anatomicopathological description of secondary petrous bone cholesteatomas, and of the CT technique used for their exploration, they describe and illustrate the classical" bag-shaped" internal or external attical forms usually extended to the antrum and the mastoid process, and the less common locations often due to relapse or postoperative recurrences (anterior hypotympanic or posterior mastoidal). The holotympanic forms, usually due to" lamellar" cholesteatomas, create diagnostic problems with other opacities in the cavity, as also do certain forms that are evacuated spontaneously or by aspiration. One of the qualities of CT lies in the preoperative extension assessment. The lesion may extend towards the internal wall of the cavity (lateral semicircular canal, second portion of the facial nerve), towards the labyrinth to the petrosal apex and/or the geniculate ganglion, and above all towards the inferior labyrinth which might bring the cholesteatoma into contact with large vessels (eg jugular vein bulb for postero-inferior extensions, carotid canal for antero-inferior extensions). Extension into anfractuosities of the cavity walls (sinus tympani, subratubal fossette) must be systematically looked for in order to avoid postoperative recurrences.