PURPOSE: To evaluate the role of MR in the diagnosis of borderline epithelial tumors of the ovary comparedwith that of benign and malignant tumors. MATERIALS AND METHODS: MR images of 42 ovarian epithelial tumors in 39patients were retrospectively analyzed, focusing on the morphologic characters distinguishing borderlineepithelial tumors from benign and malignant tumors. All images were obtained using a 1.5T imager 3-27 (mean, 12)days before surgery. The size, shape, internal signal intensity, wall and septal thickness, papillary nodule,solid component, and contrast enhancement of the tumor were evaluated. RESULTS: Histopathologic diagnoses were 16serous epithelial tumors [benign (SB) 3, borderline malignancy (SBM) 5, malignancy (SM) 8]; 24 mucinous epithelialtumors [benign (MB) 11, borderline malignancy (MBM) 9, malignant (MM) 4]; one endometrial carcinoma (EC), and oneclear cell carcinoma (CC). Mucinous epithelial tumors were multilocular in 23 of 24 tumors, while signal intensityof the locules varied in 22 of 24. Six of 16 serous epithelial tumors were unilocular, and 15 of 16 were ofhomogeneous signal intensity. Papillary projection was seen in 14 tumors (SB 1/3, SBM 5/5, SM 3/8, MB 2/11, MBM2/9, CC 1/1), but multiple (>10) projections were seen in SBM (5/5) and CC (1/1). Multiple irregular thick septawere found in 18 tumors (SM 3/8, MB 2/11, MBM 9/9, MM 4/4), while solid components were seen in ten (SM 6/8, MB1/11, MM 2/4, EC 1/1). CONCLUSION: Multiple (>10) papillary projections and multiple irregular thick septa withoutremarkable solid components are suggestive MR findings of ovarian SBM and MBM, respectively.