Odontogenic maxillary sinusitis is aetiologically different from rhinogenic maxillary sinusitis. Accordingly, there are distinct and--for the oral maxillofacial surgeon--very specific therapeutic consequences. The general clinical diagnostical principles have scarcely changed in the last years. In diagnostic imaging, computed tomography and magnetic resonance tomography are of great importance, especially concerning pre-operative diagnostics. Endoscopical techniques have been enhanced with the introduction of microcamera-supported endoscopy, a technical improvement. Therapeutical principles are: complete treatment of odontogenic factors in the whole quadrant; conservative and operative therapeutical procedures are to be combined. Other than in the ENT field, where the maxillary sinus is approached by an endo-nasal technique--infundibulotomy-in oral and maxillofacial surgery the transalveolar approach through the fossa canina is used when treating odontogenic maxillary sinusitis. However, cautious methods assuring the preservation of tissue in all respects are treatment of choice.