The sonographic and histologic findings observed in 11 cases of ovarian fibrothecoma were compared, and an attempt was made to find a correlation between each histologic type of the tumor (pure thecoma, predominantly fibrous fibrothecoma, mixed fibrothecoma) and its sonographic appearance. The presence of a homogeneous echogenic pattern, with marked posterior acoustic shadowing, in the absence of any calcification, was highly suggestive of a predominantly fibrous ovarian fibrothecoma; the presence of a diffusely hypoechoic ovarian mass, with no posterior echo enhancement, was strikingly correlated with pure thecomas; mixed fibrothecomas were characterized by the presence of an echogenic pattern with no posterior acoustic shadowing. Sonographic findings, even though nonspecific, can provide the clinician with useful information which permits to detect these rare neoplasms preoperatively.