PURPOSE: To evaluate the radiologic features of fibrothecoma of the ovary, which is a rare solid tumor originating from the ovarian sex cord-stroma. MATERIALS AND METHODS: The radiologic findings of 29 patients with pathologically-proven fibrothecoma of the ovary were retrospectively evaluated for bilaterality, size, shape, margin, echogenecity, CT attenuation, signal intensity on magnetic resonance imaging, calcification, and amount of ascites. RESULTS: All fibrothecomas were unilateral, and had well defined margins. The diameter of the mass was 4-18(mean, 9.6)cms. Elghteen of 29 tumors were round or oval with a smooth margin, and eleven were lobulated. The internal architecture of the tumor was purely solid in 21 patients, predominantly solid in six, and pre-dominantly cystic in two. A broad spectrum of sonographic features was apparent, including a homogeneously hypoechoic mass (with posterior shadowing in four cases, and without posterior shadowing in ten), a homoge-neously hyperechoic mass in seven cases, an anechoic mass with septatations in two, and a mixed echoic mass in six. On precontrast CT scans, the mass was isodense to the uterine myometrium in eight of nine cases, while on postcontrast scans the lesion was slightly hypodense to the myometrium in seven cases and isodense in one. On T1-weighted MR images, nine of ten cases showed a relatively homogeneous low signal intensity, while on T2-weighted images, signal intensity was homogeneously low in two patients and predominantly low with focal high intensity in seven of the other eight. On gadolinium-enhanced T1-weighted images, most tu-mors showed slight heterogeneous enhancement. Calcifications were present in two cases, and in two others there was a large amount of ascites. CONCLUSION: The characteristic finding of ovarian fibrothecomas is a well-defined, oval or lobulated homoge-neously solid mass, which on CT scans enhances less than uterine myometrium and demonstrates a predomi-nantly low signal intensity on both T1- and T2-weighted images. However, a predominantly solid mass with cystic components or a predominantly cystic mass may also be presented.