Dentigerous cyst is the second most common odontogenic cyst and is associated with the crown of an unerupted tooth. Removal of the entire cyst with the impacted tooth is a treatment of choice to prevent recurrence. Although Caldwell-Luc approach has been used frequently for the treatment of a dentigerous cyst in the maxillary sinus, it has more morbidity than transnasal endoscopic approach. Moreover, endoscopic approach has several other advantages, such as good illumination, clear and magnified visualization, resulting in more conservative surgery with pre-cise dissection. A 37-year-old man was referred to the outpatient clinic due to an incidental large expansile cystic lesion containing ectopic tooth in the right maxillary sinus. Endoscopic examination identified a prominent bulging lesion in the inferior meatus. The cyst with the tooth was removed completely through a large inferior meatal antrostomy with endoscopic guidance. Postoperative course was uneventful and there was no recurrence for 4 years postoperatively.