The histogenesis of benign mucosal tumors of the nose and paranasal sinuses is reviewed in this report. In contradistinction to the view favored in the literature, these comprise three distinct entities. Everted and cylindric cell papillomas are true papillomas, lined by stratified squamous and microcyst-laden, columnar, and oncocytic epithelium, respectively. Inverted papillomas are polyps with marked, patchy squamous metaplasia in ductal and surface epithelium and numerous microcysts containing macrophages in those epithelia. Low-grade squamous carcinoma of the nose and paranasal sinuses may be difficult to distinguish from inverted papilloma. There are no intermediate forms from any one of the three types of benign mucosal tumors of the nose and paranasal sinuses to another. The site of origin of everted papilloma is from the nasal septum or nasal vestibular epithelium. Inverted and cylindric cell papillomas arise on the other hand from the lateral wall of the nose, ethmoid, or maxillary sinuses. Inverted papillomas alone among the three have a strong tendency to recur, and some cases are associated with carcinoma, although the development of malignancy is unusual.