The purposes of this study Were to compare transvaginal sonographic scanning of the uterus and endometrium with histology obtained by endometrial biopsy or curettage and to determine whether the sonographic technique might be useful in the evaluation of postmenopausal women. Eighty postmenopausal women were studied. of these, 65 were asymptomatic (38 on no hormone therapy and 27 on hormone replacement). Fifteen women underwent evaluation because of postmenopausal bleeding. In both groups, endometrial thickness of 4 mm or less as depicted by sonography correlated well with endometrial characteristics of decreased estrogen stimulation. However, in Women with measured endometrial thickness between 5–8 mm, proliferative endometrium could not be distinguished from hyperplastic endometrium or, in one case, low-grade carcinoma. Large polyps and invasive carcinoma with myometrial extension were easily recognized. © 1991 by The American College of Obstetricians and Gynecologists.