Purpose : To compare CT and US features of immature and mature teratomas of the ovary. Materials and Methods :We retrospectively reviewed CT and US findings of 11 patients with immature teratoma and 18 patients(20 cases)with mature teratoma. The tumors were classified into three groups on the basis of image findings : predominantlycystic(type I), predominantly solid(type II), and mixed cystic and solid(type III). Result : All eleven cases ofimmature teratoma were of the mixed type(type III), showing multiple small(less than 2 cm) nodular and linearcalcifications and fatty nodules within the solid component and adjacent to the septa of the cystic component ofthe masses. In contrast, mature teratomas were predominantly cystic in six cases, predominantly solid in eight,and mixed in six cases. In five of six mixed type mature teratomes, calcified fatty nodules were fewer and largerthan in immature teratomas. Conclusion : Immature teratoma may be diagnosed by the demonstration on CT or US ofmultiple small(less than 2cm) nodular and linear calcifications and fatty nodules in the solid and cysticcomponents of the tumor.