Anatomic variations of the nasal cavity and paranasal sinuses are described in order of their appearance in endoscopy. Variations of the pyriform aperture are followed by variations of the agger nasi, inferior and middle conchas, inferior and middle nasal meati, and variations of the bulla ethmoidea, uncinate process and fontanelles. Variations of the maxillary sinus are described from their anterior and lateral views. Partial and total septation of the maxillary sinus, variations of its dimensions and its relation to dental roots are stressed. The dimensions of the frontal sinus, frontal bulla or bullae are noted. The variation of the sphenoid sinus and its dimensions and relationships to the structures of the cavernous sinus and the endocranium are described. Pneumatization of the anterior clinoid process and the region around the optic canal by the frontal sinus, ethmoid labyrinth or sphenoid sinus is discussed. Knowledge of these different variations will help the rhinologic surgeon in his orientation during endoscopic surgical interventions.