Most subdural hematoma with significantly differed attenuation from that of adjacent brain tissue can be accurately diagnosed by CT. Difficulty arises when the hematoma is isodense that is exhibited similar attenuation to that of brain. Unilateral isodense subdural hematoma can be identified by indirect isodense subdural hematomas has met with variable success. Moreover, bilateral isodense subdural hematoma may be more difficult. We therfore considered it of interest to evaluate the diagnositic efficiency fo CT in isodense subdural hematomas. We have analysed 13 cases surgically provenced cases of isodense subdural hematoma examined at Korea General Hospital from October 1981 to April 1982. The results were as follows : 1. One hundred twenty seven cases of subdural hematomas were studied by CT, 13 cases (10.2%) of which were isodense. 2. The age distribution was from 29 years to 69 years and mean age was 52 years. The sex ratio was 11 mate to 2 female. 3. Seven (53.8%) of 13 cases has a history of head trauma. 4. The time interval which subdural hematoma became isodense was from 1 week to 4 months and peak time interval was from 1 week to 3 week. 5. The precontrast CT scan of isodense subdural hematoma appeared shifting of midline structure, compression and deformity of the ventricles in all 13 cases, effacement of cerebral sulci in 10 cases compression and deformity of the ventricles in all 13 cases effacement of cerebral sulci in 10 cases (76.9%) and dilatation of contralateral ventricles in 4 cases (30.8%). 6. The postcontrast CT scan demonstrated enhancement of the medial margin of the lesion in 4 (30.8%) of 13 cases and displacement of cortical vein away from the inner table of the skull in 3 (23.1%) of 13 cases. 7. Bilateral isodense subdural hematomas were 2 (15.4%) of 13 cases.