Dermoid cyst of the floor of the mouth is rare. The majority of dermoids are developmental cysts derivered from epithelial debris or rest enclaved during the midline closure of the bilateral mandibular (first) and hyoid (second) branchial arches. Most often it occurs shortly after birth, the development of these cyst occurs during the period of increased activity of epithelial tissues. The increased activity of the growth coincidenced with the ages of 15 to 35 years, when most of these lesion occurs. They project into the floor of the mouth or into the neck behind the chin, or both places. Recently the authors had experienced a dermoid cyst of the floor of the mouth.