Dentigerous cysts are the common type of developmental odontogenic cyst that encloses the crown of unerupted tooth. Dentigerous cyst develops by the accumulation of fluid between reduced enamel epithelium and tooth crown and is attached to the tooth at cemento-enamel junction. They are more common in males than in females and occurs mostly in permanent dentition. The majority of dentigerous cysts involves mandibular third molars, maxillary canines, mandibular premolars and maxillary third molars. This article presents a case of unilateral mandibular dentigerous cyst associated with impacted mandibular third molar in a patient treated by enucleation.