Reported cases of a large dentigerous cyst involving the whole maxillary sinus are uncommon. A 22-year-old female patient suffering from swelling of the right infraorbital area and cheek with dull pain was referred to our department. Findings on computed tomography (CT) and magnetic resonance imaging (MRI) revealed a huge mass containing a displaced maxillary third molar involving the right maxillary sinus as a whole, with partial erosion of the posterior sinus cortical bone. Under general anesthesia, the mass was enucleated using the Caldwell-Luc approach, and, following histopathological analysis, was diagnosed as a dentigerous cyst. The case was followed for a period of seven years, and no evidence of sinus infection or recurring cyst formation was observed during that time.