We report the case of a 19-year-old female presented with a subcutaneous mass in the right posterior thigh for 2 months, which was later confirmed as immature teratoma (CK5/6<sup>+</sup>, CK8/18<sup>+</sup>, CK7<sup>+</sup>, CK20<sup>+</sup>, villin <sup>+</sup>, S-100<sup>+</sup>, Syn<sup>+</sup>, GFAP<sup>+</sup>, NF<sup>+</sup>, Neu-N<sup>+</sup>, CgA<sup>+</sup>, CD99<sup>+</sup>, Dasmin<sup>-</sup>, SMA<sup>-</sup>) with higher expression of Ki-67. Here, CD99 is linked to teratoma.