From November 1987 to April 1989, 1000 women 40 years or older underwent screening vaginal sonography at the University of Kentucky Medical Center (Lexington, KY). Patients included in this investigation were all asymptomatic and had no known pelvic abnormalities. Each ovary was measured in three planes and ovarian volume was calculated using the prolate ellipsoid formula. The upper limit of normal for ovarian volume was 18 cm3 in premenopausal women and 8 cm3 in postmenopausal women. In patients with normal scans, mean ovarian volumes decreased from 6.8 cm3 to 3.0 cm3 with menopause. Thirty-one patients (3.1%) had abnormal vaginal sonograms and 24 underwent exploratory laparotomy. All patients undergoing surgery had ovarian or fallopian tube tumors with dimensions identical to those predicted by ultrasound. Histologic diagnoses of these tumors included the following: adenocarcinoma, one, serous cystadenoma, eight; endometrioma, six; and cystic teratomas, two. Vaginal sonography was performed easily and without complications, and was well accepted by patients. All patients with normal sonograms have been rescreened annually and none have subsequently developed ovarian cancer. Further clinical trials to determine the efficacy of vaginal sonography as a screening method for ovarian cancer are indicated.