To find the chaaracteristic computed tomographic findings of inverted papilloma and the point of differential diagnosis with benign inverted papilloma and inverted papilloma associated with malignancy, the authors retrospectively evaluated 15 patiented 15 patients with histologically confirmed malignancy(4 patients) in Severance Hospital from January 1986 to February 1990. Transitional cell carcinoma(2 patients), squamous cell carcinoma(1 patient), and undifferentiated cell carcinoma(1 patient) were associated with inverted papilloma. The typical mass arose from the lateral nasal wall of the middle meatus extending into the antrum of ethmoid sinus, and the density of the mass was inhomogenous with a slightly higher attenuation than that of the muscle in 13 patients on the contrast enhanced CT scan. The bone changes were nonspecific, because pressure erosion, remodeling, or sclerotic changes in 14 patients, and the purely destructive change of planum sphnoidale was seen in the patient with benign inverted papilloma. Extension beyond the nasal cavity and paranasal sinuses such as pterygopalatine fossa or nasopharynx was seen in 5 patients, 3 of whom had a coexisting malignancy. The moderate inhomogenous mass in the nasal cavity and paranasal sinuses with pressure erosion or sclerosis of the adjacent bony structures could suggest inverted papilloma, and a coexisting malignancy may be considered when extension beyond the nose and paranasal sinuses are demonstrated.