Polymorphous low-grade adenocarcinoma (PLGA) is a rare tumor, mostly affecting the minor salivary glands of the oral cavity. We report a case of PLGA which occurred within the maxillary sinus in a 59-year-old woman. The tumor was resected through a transnasal endoscopic approach with wide margins. To the best of our knowledge, this is the first reported case with primary PLGA of the maxillary sinus.