Dermoid cysts on the floor of the mouth are reported to account for less than 2% of all dermoid cysts. These cysts of the floor of the mouth are classified by the Bergmann-Hagisaki classification into the sublingual type, submental type or sublingual-submental type based on their positional relationship with the oral structures. This classification is important for determining the appropriate surgical strategy. The cyst size and cyst position are also important considerations for selecting the appropriate surgical strategy. We encountered two cases of dermoid cysts of the floor of the mouth at our department, and present these cases here with some bibliographic consideration. The diagnosis in both cases was made by imaging and histopathology. The MRI findings were characteristic; we recognized a cyst with a clear margin and the sack-of-marbles appearance, visualized as low signal intensities on T1-weighted images, and as high intensites on T2-weighted images. The cyst in case 1 was diagnosed as being of the sublingual-submental type from the MR images. It was resected via the cervical approach. The cyst in case 2 was diagnosed as being of the sublingual type, and was safely resected via the transoral approach. If we can obtain a field of view taking into consideration the size and position of the cyst, we believe that it is possible to satisfactorily excise the cyst via approach from a single side.
