Dentigerous cysts are closed epithelium-lined sacs formed about the crowns of unerupted teeth. Most of them probably are the result of degenerative changes in the reduced enamel epithelium. The authors observed 1 3 year old girl with a swelling and buccal bony expansion of the left mandible. Roentgen examination showed a cystic area in the left side of mandible. Under general anesthesia by means of nasotracheal intubation, intraorally, the operation by enucleation consisted in surgical removal of dentigerous cyst and the left unerupted Ist molar of mandible. The cavity was partially sutured and packed with iodoform gauze. Healing was uneventful.