Seventeen cases of intrauterine fluid collections in postmenopausal women demonstrated by sonography were collected. Of the 17, 16 (94%) were found to have active carcinoma involving the uterine corpus or cervix. Eleven (65%) had cervical stenosis due to previous surgery, radiation therapy, or carcinoma. The fluid collected was pus, blood, or serous or serosanguineous fluid, and tumor nearly filled the dilated uterine cavity in some cases. The sonographic demonstration of a distended uterine cavity in a postmenopausal woman suggests carcinoma involving the uterus.