Dentigerous cysts are the most common type of developmental odontogenic cysts. They form as a result of a separation of the follicle from around the crown of an unerupted tooth. Usually this lesion can be asymptomatic. Such cysts are often discovered accidently on inspection of x-rays. In other advanced cases, cortical bone expansion, displacement of teeth, secondary infection can be observed. The treatment of dentigerous cyst is enucleation. And according to size, location of lesion and environmental structure marsupialization can be considered. However, Marsupialization takes long treatment time and, cystic tissues are remained so secondary surgery may be needed for total removal., Risks of oroantral fistula, damage on maxillary sinus wall and infraorbital nerve can be considered as complications of conventional surgical treatment of cysts located in maxillary sinus. We treated third molar origin dentogerous cyst located in maxillary sinus removing endoscopically both the tooth and an associated dentigerous cyst. We report our clinical experience with literature review.