PURPOSE: To evaluate the usefulness of MRI findings in the differentiation of benign from malignant ovarian lesions. MATERIALS AND METHODS: Using MR findings, 29 surgically proven ovarian masses in 22 patients (14 bilateral tumors) were evaluated Twenty-one benign tumors in 16 patients (5 simple cysts, 4 mucinous cystadenomas, 4 serous cystadenomas, 4 endometriomas, 3 cystic teratomas and 1 tuboovarian abscess), and eight malignant tumors in six patients (4 serous papillary cystadenocarcinomas and 4 mucinous cystadenocarcinomas) were included. MRI was performed with SE T1WI, FSE T2WI and Gd-T1WI. MRI findings of lesion size, thickness of wall and of internal septations, number of internal septations, nodularities, and ancillary findings such as adhesion in the pelvic cavity, dissemination, ascites and lymphadenopathy were retrospectively analyzed. RESULTS: Malignant ovarian lesions were larger (18 cm : 11 cm) and had more internal septations, more solid components and nodularities (63 % : 5 %) than benign lesions. On T1WI, cystic lesions, both benign and malignant, showed low signal intensity. Hemorrhage, fat components and mucin containing lesions showed high signals and solid components and nodularities were isointense with muscle on T1WI. Solid components and nodularities were well-enhanced after gadolinium enhancement. Adhesion (50 % : 10 %), dissemination (38 % : 0 %) and ascites (63 % : 24 %) were more frequent in malignant lesions. CONCLUSION: MRI, especially with gadolinium-enhanced T1W1 is useful in the differentiation of benign from malignant ovarian lesions.