For populations in which preventive measures have been applied for the more common causes of death, the early detection of ovarian cancer becomes the next focus of efforts to reduce premature death among women. Data regarding the effectiveness of ultrasonography in detecting early-stage ovarian cancer are reviewed. Ultrasonography is more sensitive than pelvic examination in detecting ovarian abnormalities but lacks specificity in distinguishing benign from malignant ovarian lesions. Combined with serum CA 125 levels, ultrasonography may provide an effective screening tool, although cost-effectiveness has not been demonstrated and its effectiveness in reducing mortality from ovarian cancer has not been completely evaluated. Guidelines are presented for the use of ultrasonography in evaluating the postmenopausal ovary. © 1991 by The American College of Obstetricians and Gynecologists.