PURPOSE: The purpose of this study is to find helpful MR findings for predicting a naplastic oligodendrogl lomas. MATERIALS AND METHODS: Retrospective analysis of 46 MR images and 37 CT scans was performed for 46 patients with pathologically-proven cerebral oligodendrogliomas. A neuropathologist graded the tumors as one of low-grade (n=16), intermediate-grade (n=l2), or anaplastic oligodendroglioma (n=18). MR imaging features were retrospectively analysed with respect to histologic grading of the tumors. RESULTS: Contrast enhancement was observed always in anaplastic group (17 /17), in a portion of intermediate-grade group (4/10) but not in low-grade group (0/14). Peritumoral edema was observed infrequently in anaplastic group (4/18) or intermediate-grade group (1/12). Cystic changes (25/46) or calcifications on CT Scans (14/37) were not related with histologic grading. Grossly identifiable hemorrhage was rare in this series (2/46). Among the various imaging features, only tumor enhancement and peritumoral edema were statistically significant for trend test (p<0.05). CONCLUSION: When considering the diagnosis of oligodendrogliomas, the presence of contrast enhancement or peritumoral edema is a helpful features suggesting anaplastic oligodendrogliomas.