PURPOSE: The purpose of this study is to correlate CT findings of the patients with chronic subdural hematoma(SDH) showing a sedimentation level with their clinical and operative findings. MATERIALS AND METHODS: We selected 9 patients who showed a sedimentation level within the hematoma after reviewing the CT findings of 55 patients with SDH. We also analyzed their age, initial symptoms, cause of head injury, latent period, the level of consciousness on admission, CT findings, and operative findings. RESULTS: All of the 9 patients were aged persons(over 52 years). They had a history of acute exacerbation of neurologic symptoms. Five of them had an apparent history of head trauma more than one month before the exacerbation. The CT scans showed unilateral, crescent-shaped subdural fluid collection with a sedimentation level except a case of bilateral SDH and 2 cases of planoconvex-shaped SDH. The interface of the sedimentation level was sharp in 3 cases and indistinct in 6 cases. None had bleeding tendency and the hemoglobin level was slightly decreased in 2 patients. All patients revealed membrane of the hematoma during operation. The upper portion of the sedimentation was liquefied blood and the lower portion was fresh blood clots. We could observe fresh RBC's in the hematoma microscopically. CONCLUSION: A sedimentation level in chronic SDH was operatively proved to represent rebleeding, and was clinically manifested as an acute exacerbation of symptoms.