Teratomas are germ-cell tumors commonly composed of multiple cell types derived from one or more of the three germ layers. They derive from embryonic pluripotent cells and may have various degrees of maturation, according to which they are classified as mature, immature, and malignant. Teratomas are found with decreasing frequency in the ovaries and testis, mediastinum, retroperitoneal space, sacrococcygeal zone, pineal and other intracranial locations.