Standard radiographs are suboptimal in the display of the regional morphology in the nasal cavity and paranasal sinuses, especially the ethmoid sinus. The preferred radiographic modality for the evaluation of the nasal cavity and paranasal sinuses is computed tomography (CT). Coronal CT imaging perpendicular to the bony palate affords the best display of the ostiomeatal channels and facilitates the surgeon's perception of this regional morphology because it most closely resembles the endoscopic view. The purpose of this article is to familiarize the reader with the regional anatomy of the nasal cavity and paranasal sinuses, specifically the 14 anatomic structures the examiner must understand and systematically check in the evaluation of this morphologic area. A description of the most commonly found anatomic variations that influence the patency of the ostiomeatal channels as well as specific relationships between the paranasal sinuses, the orbits, and the intracranial compartment are also detailed. Although less helpful in the display of paranasal sinus chronic inflammatory disease, magnetic resonance imaging is beneficial in the diagnosis of fungal disease, neoplastic disease, and the display of inflammatory extension into the intracranial and intraorbital compartments.