In 14 cases of diffuse astrocytoma, glioblastoma and cerebral lymphoma CT was compared to the gross anatomy and their histology at corresponding levels. Diffuse spread of tumor even in areas of considerable increase of cellular density are not recognizable in CT including application of contrast medium. Circumscribed and frequently multiple foci inside of diffuse areas of gliomatosis may have necrosis and extensive vascular changes including haemorrhage. These foci alone are demonstrable by pathological changes in CT and may suggest multiple metastatic growth or vascular lesions. True unconnected multiple lesions in gliomas are rare as can be demonstrated by intensive histological investigations but occur in cerebral lymphomas.