This paper presents the cranial CT and MR imaging studies of a 68-year-old female with intermittent headaches in the left parietal region, with diffuse expansion, and fatty replacement of the red marrow of the entire left parietal diploe, which revealed negative attenuation values on CT (-60 H.U.) while this value in the contralateral diploe was very high (+450 H.U). The condition was verified by biopsy. The suggested name for this pathology is 'diploic lipomatosis' because of diffuse involvement of the left parietal diploe resulting in expansion and partial resorption of the diploic trabeculae. The patient did not have asymmetry of the cerebral hemispheres. The condition was compared with that of twenty craniocerebral hemiatrophy (Dyke-Davidoff-Masson syndrome) patients. These patients had unilateral loss of cerebral volume with widening of the ipsilateral diploe, CT attenuation values of which were high (mean= +420 H.U.). It appears that Òdiploic ilpomatosis' is a new clinical entity unrelated to craniocerebral hemiatrophy.