[en] High resolution computed tomography (HRCT) and three dimensional CT (3DCT) were performed in 9 patients with chronic osteomyelitis of the mandible and 2 patients with gingival carcinoma. The periosteal reaction was seen only in the osteomyelitis cases. The irregular destruction of the cortical bone was seen mainly in the malignant cases. The sclerotic change was severer in the osteomyelitis than in the malignant tumor. The extension and the shape of the lesion could be evaluated accurately by HRCT and 3DCT and the soft-tissue changes were also revealed clearly by the soft-tissue mode of the HRCT. (author)