Teratoid cyst was first proposed by Meyer in his classification of dysontogenetic cysts of the floor of the mouth. We report a case of congenital teratoid cyst in the floor of the mouth. A 9-day-old boy was referred to us because of congenital swelling of the floor of the mouth. On examination, a hemispherical 25 mm ×25 mm elastic soft, fluctuant mass was observed in the floor of the mouth. On examination of the mass fluid by exploratory puncture, the amylase level was 87 IU/ℓ. Clinically, the lesion was diagnosed as a cyst other than ranula. Therefore, surgical removal of the cyst was performed at 6 months of age. Histopathological examination revealed a teratoid cyst that contained squamous epithelium, hair follicles, sebaeceous glands, sweat glands, fat, salivary gland tissue, striated muscle, and respiratory and gastrointestinal epithelium.
