Both the structural and functional roles of the paranasal sinuses in animals still remain controversial. The external nose and nasal fossae developed so as to offer mechanisms to prevent inundation of the airway while the importance of olfactory mucosa in carnivora has increased. The location of the nostrils on the upper part of the head and the appearance of the nasal valve are significant achievements for defending against water entrance in the airways. Nasal conchae, observed also in amphibia, reptilia and birds, yield warming and moistening of inhaled air. The ethmoidal conchae are responsible for olfaction, as well as the majority of the mucosa lining the maxillary, frontal and sphenoidal sinuses in carnivora. Gorilla and man are the only species that possess large non-olfactory sphenoidal sinuses, and man is the only to present a true ethmoidal labyrinth. There is scant evidence that paranasal sinuses are responsible for skull lightening, voice resonance, facial growth, air conditioning, mucus production, brain thermal insulation and olfaction in the human being. There are clues that the paranasal sinuses might have physiologic and structural role in the synthesis and storage of nitric oxide as part of the airway defense mechanisms.