Cylindrical cell papilloma (CCP) is the rarest of three morphologically distinct papillomas that occur in the nose and paranasal sinuses. Because it is unfamiliar to many pathologists, it is often mistaken histologically for papillary adenocarcinoma or even rhinosporidiosis. The clinical and pathologic features of six new cases are reported and compared with those of 14 others reported in the literature. The results of the light microscopic, histochemical, immunocytochemical (cytochrome c oxidase), and ultrastructural studies described here provide conclusive evidence that the swollen, granular, eosinophilic epithelial cells that compose CCP are true oncocytes that arise primarily, or perhaps exclusively, from the respiratory (Schneiderian) epithelium of the sinonasal passages rather than from minor salivary glands. Continued designation of the CCP as such should therefore be discouraged in favor of a more precise term reflecting this derivation. The phrase "oncocytic Schneiderian papilloma" is proposed.