The cyst of the maxillary sinus is rare disease and can be divided into two groups ; one having relation to teeth etiologically and anatomically and the other no relation with them. Recently, the author have experienced a case of dentigerous cyst in the right maxillary sinus accompanied with eustachian salpingitis on the same side. The cyst mass was completely removed under general anesthesia by Caldwell-Luc's approach. Histopathological study demonstrated a dentigerous cyst.