A 19-year-old man was referred to Seoul National University Dental Hospital for evaluation of a large painless swelling of the left mandibular angle area in August, 1999. The growth had been first noted 6 years ago. He had visited other hospital in 1997. In spite of the treatment given at the hospital, the mass continued to grow rapidly. Conventional radiographs in 1999 showed an expansile, lobulated, and destructive lesion of the left mandibular body. CT scan demonstrated an expansile mass with a corticated margin. Bony septa were seen within the lesion. Internal calcification noted on the bone-setting CT image, and corresponded to the hypointense area in T1-weighted MRI image. MRI clearly delineated the extent of the lesion which had heterogenous intermediate signal intensity in T1-weighted images and heterogenous hyperintense signal intensity in T2-weighted images. The lesion was well-enhanced. Histopathologically, the lesion was well demarcated. Multinucleated giant cells were presented in a fibrous background, demonstrating a storiform pattern. Areas of osteoid rimmed by a few osteoblasts were scattered throughout the lesion. Inflammatory cells, blood vessels, and hemosiderin deposition were also shown. CGCG may show lots of internal calcification foci on the CT, and varied signal intensity in MRI. More cases will be needed to understand the features of the CT & MR finding of CGCG.