Dermoid cysts of the head and neck account for nearly 7% of all dermoid cysts and of these, 23% were in the floor of the mouth. Most dermoid cysts in the floor of the mouth are derived from epithelial debris or rests enclaved during the midline closure of the bilateral first and second branchial arches. In the head and neck, dermoid cyst may apply to three varieties of cysts : (1) epidermoid or epidermal cyst ; (2) dermoid cyst ; and (3) tratoid cyst. The epidermoid variety is most common. Dermoid cysts generally become manifest during the second and third decades of life. In contrast, epidermoid cysts are more common in infants. Neither the epidermoid nor the dermoid cyst exhibits any sex predilection. Treatment is complete surgical removal ; the prognosis is excellent. We experienced recently a case of epidermoid cyst of the floor of the mouth.