Miyazaki T, et al. - The clinical features of inverted papilloma (IP) as it relates to malignancy were determiined. The therapeutic strategy and clinical course of malignant IP were determined. Among IP patients presenting with nasal bleeding, pain, and bone destruction pre-operatively, a complication with malignancy should be suspected and treatment should be planned. Even if malignancy was not confirmed on postoperative histology, careful observation should be ensured because of metachronous malignant transformation or the possibility to overlook small malignant lesions.