Primary Fallopian tube carcinoma (FTC) is one of the rarest gynecological malignancies, accounting for 0.18% to 1.6% of all malignant neoplasms of the female reproductive tract. Preoperative diagnosis of FTC has been previously reported; however, most patients with FTC undergo laparotomy with a presumed diagnosis of ovarian carcinoma. The final diagnosis of FTC is usually established at the time of surgery or on pathological examination. To our knowledge, this is the first report in the English scientific literature in which the preoperative diagnosis of FTC was established by the presence of an adnexal mass with an incomplete septation on transvaginal sonography. Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.