This document provides information about the maxillary air sinus (antrum). It discusses the embryology, anatomy, functions, clinical importance and diseases of the maxillary sinus. The maxillary sinus begins developing in the fourth month of gestation and reaches adult size by age 18. It is pyramidal in shape with thin walls. Diseases discussed include acute and chronic sinusitis, polyps, cysts and tumors. Surgical procedures for treating maxillary sinus diseases like antral lavage and Caldwell-Luc operation are also summarized.