A 25-year-old virginal Japanese woman underwent surgery for an ovarian tumor that was diagnosed as a mature teratoma. A solid mass within the tumor was found to have a head, trunk, and extremities. Consequently, this mass was diagnosed as a mature fetiform teratoma (homunculus). Brain, eye, spinal nerve, ear, teeth, thyroid gland, bone, bone marrow, gut, trachea, blood vessels, and phallic cavernous tissue were confirmed microscopically. Distinctive features were the clear anterior-posterior, ventral-dorsal, and left-right axes, with a spatially well-organized arrangement of the organs. An eye was located on the front of the head, a spinal nerve lay dorsal to the spinal bones, the thyroid gland was anterior to the trachea, and the gut was deep inside the trunk.