PURPOSE: To evaluate the findings and differential points of ovarian fibroma and subserosal leiomyoma, as seen on MR images. MATERIALS AND METHODS: The MR imaging findings of 31 surgically confirmed cases of ovarian fibroma(n=6) and subserosal leiomyoma (n=25 ; 28 lesions) were evaluated. Multiplanar T1- and T2-weighted and postcon-trast T1-weighted images were obtained using a 1.5T MR unit, and histologic examination was also performed. The MR findings were analyzed in terms of signal intensity, the presence and definition of margin, the histo-logic finding of hyperintense lesion on T2-weighted images, the presence of the bridging vessel sign, degree of enhancement, and the presence of ipsilateral ovary and ascites. RESULTS: Both fibromas and leiomyomas showed hypo-or isointensity compared with uterine myometrium on T1-weighted images and compared with skeletal muscle on T2-weighted images. The latter revealed intratu-moral hyperintense lesions in most cases of ovarian fibroma and subserosal leiomyoma. Three of four ovarian fibromas had a well defined margin after cystic change, but in 24 of 26 subserosal leiomyomas the margin was ill defined. The "bridging vessel sign" was visible only in subserosal leiomyomas (22/28), and in all cases the enhancement of ovarian fibromas were less than that of myomtetrium. Subserosal leiomyomas (12/28), seen on enhancement as isointense or hyperintense to myometrium, showed a greater degree of enhancement than ovarian fibromas (0/6). Ipsilateral ovary was rarely seen in ovarian fibromas (1/6), but commonly seen in sub-serosal leiomyomas (20/25). Ascites was present in one case of ovarian fibroma. CONCLUSION: A defined margin of an intratumoral hyperintense lesion, as seen on T2-weighted images, and the presence or absence of the "bridging vessel sign" and ipsilateral ovary are useful signs when differentiating be-tween ovarian fibromas and subserosal leiomyomas.