The anatomy of maxillary ostium is highly variable in size, shape and position. The endoscopic sinus surgeons should have detailed knowledge about variations of maxillary sinus opening in any endoscopic sinus surgeries as it is closely related to the orbital floor above, sphenopalatine artery posteriorly and nasolacrimal duct anteriorly. We report a case of abnormal location of natural maxillary sinus ostium at extreme posterior tip of infundibulum, which was identified during functional endoscopic sinus surgery and managed successfully.

Keywords: Maxillary sinus Ostium; sphenopalatine artery.