Subdural hematomas are relatively common and the typical CT findings according to the age of them are well established. The CT findings of 82 patients with SDHs were reviewed and compared with the operative findings, RESULTS : 1. The most common cause of SDHs was the direct trauma which was noted in 60 cases. 2. The atypical CT findings of the mixed density were seen in 19 cass, including acute SDH 7 cases, subacute SDH 5 cases, and chronic SDH 7 cases. 3. The possible casuses of the mixed density in acute SDH were unclotted blood in early stage of hematoma development or serum extruded during the early phase of clot retraction. But the possibility of cerebrospinal fluid within subdural space due to an arachnoid tear could not be exclued. 4. The possible causes of the mixed density in subacute and chronic SDH were serum extruded during the hematoma resolution and rebleeding. 5. Wall enhancement of hematomas was notedin 3 cases of subacute SDHs and 15 cases of chronic SDHs. 6. ost of SDHs was crescentic in shape, but lenticular in 4 cases. Midline shift and compression of ventricles were proportional to the maximum thickness of SDHs. There were seen ipsilateral dilatation of ventricle in 9 cases and brain edema in 11 cases.