Dermoid cysts of the floor of the mouth are rare lesions thought to be caused by entrapment of germinal epithelium during the closure of the mandibular and hyoid branchial arches. They usually present as a nonpainful swelling. This type of lesion occurs more frequently in patients between 15 and 35 years, but can be seen in all age ranges. Histologically, all dermoids are lined by epidermis. The contents of the cyst lining determine the histological categories of the cyst: epidermoid, if epidermis is lining the cyst; dermoid, if skin annexes exist; or teratoid, if there are tissues derivated from the three germinal layers. Anatomical classification is useful for surgical approach choice, intra- or extraorally. This report presents a case of a dermoid cyst of the floor of the mouth in a 12-year-old patient, and a review of all steps necessary for its diagnosis and treatment was made.