This study proposes a new staging system for cancer of the paranasal sinuses on the basis of two concepts. The first concept is that the nasal cavity and the paranasal sinuses form a single unit. Consequently, the mucosa of each sinus may give rise to tumors. The histopathologic variation will be the same for all these cavities. The second concept is that the staging of these tumors depends both on the nature of the neoplastic cells and on the specific bone boundaries which surround the anatomic site and subsites. We analyzed 61 cases and we emphasize the need for a differential analysis of T4 tumors depending on which adjacent region is involved.