PURPOSE:To evaluate CT and MR findings suggestive of inverted papilloma by correlation with pathologic findings. MATERIALS AND METHODS: The CT(n=16) and MR(n=8) findings of 22 pathologically proven cases of inverted papilloma in the sinonasal cavity were retrospectively reviewed with reference to location of tumor, density/signal intensity, contrast enhanced appearance, shape and cleft air shadow at the free margin of tumors, and mass effect. These findings and pathologic findings were then correlated. RESULTS: All 22 tumors were located in the unilateral nasal cavity and extended into the maxillary sinus(n=17), choana(n=10), ethmoid sinus(n=8), nasopharynx(n=7), nasal vestibule(n=5) or frontal sinus(n=1). All CT scans showed that the density of tumor masses was similar to adjacent muscle. Precontrast CT scans showed no visibles triations' within the tumor mass, but postcontrast scans revealed striations' of varying degree in six of nine cases. CT scans showed that the free margin of tumors was serrated(n=13) or lobulated(n=5), and in 13 cases cleft air shadow of varying shape was noted. All MR scans showed's triations' with intermediate/slightly high signal intensity on T1WI and intermediate/high on T2WI within tumor masses, which were more prominent on postcontrast scans. On MR, the free margin of tumors was seen to be serrated(n=5), lobulated(n=4), or smooth(n=1), but cleft air shadow was not detected. CONCLUSION: The triations' seen on postcontrast CT and MR images and the cleft air shadow with a serrated appearance seen on CT images at the free margin of tumors suggested the presence of inverted papilloma in the sinonasal cavity.