The odontogenic cyst is not rare in the maxillary sinus. However, it is rare that the cyst completely fills and expands the maxillary sinus and becomes the giant cyst. In the lecture, it was presented a dentigerous cyst appeared as the right midfacial swelling and narrowed the right nasal cavity and expanded to the ethmoid sinuses. The cyst was extracted completely with guided endoscopy as a surgical therapy. The reason for presenting the case is to emphasize that to combine classical surgical methods with modern methods increases efficiency and reliability in the surgical therapy.