AbstractThree cases of keratosis obturans, which were studied by tomography of the petrous temporal bone, are described. The widening of the deep bony part of the external auditory canal by pressure erosion of an impacted benign slowlygrowing mass is the key radiological finding. Erosion was so severe as to involve the facial nerve canal in one and the temporo-mandibular joint in two cases. The theories of causation are reviewed. Tomography using elliptical tube movement was valuable in diagnosis, pre- and post-operative management.