PURPOSE: To evaluate the radiologic features of endodermal sinus tumor of the ovary. MATERIALS AND METHODS:The radiologic findings of eight patients with pathologically-proven endodermal sinus tumor of the ovary wereretrospectively evaluated for bilaterality, size, margin, architecture, septa, local invasion, distant metastasis,ascites and lymphadenopathy ; serum alpha-FP was also evaluated. RESULTS: All endodermal sinus tumors were unilateralwith irregular septa and ascites ; the longest diameter was 7-18(mean, 12.6)cm. Four of eight tumors had smoothmargins and four, lobulated. Four were predominantly cystic in internal architecture, one was purely cystic, andthree were predominantly solid. There was local invasion or distant metastasis in three patients, andretroperitoneal lymphadenopathy in one ; in seven cases, alpha-FP level was more than 1.000ng/ml. CONCLUSION: Endodermal sinus tumors of the ovary appeared as nonspecific large complex abdominal masses and it was difficultto differentiate them from other malignant ovarian tumors. This tumor should be included in the differentialdiagnosis of a large complex abdominal mass in girls and young women, especially in patients with a predominantlycystic mass and markedly elevated serum alpha-FP.