Ten patients were studied in whom precontrast computed tomography (CT) revealed an isodense mass which obliterated cerebral sulci and deformed the ventricle(s). Upon rapid-high-dose (RHD) contrast enhancement, the cerebral hemispheric surface was so well demonstrated, that in 4 patients the possibility of an isodense subdural hematoma was excluded, while in the other 6 it was correctly diagnosed. Preoperative angiography was not necessary.