Aims: To determine the cut-off level of endometrial thickness for detecting endometrial disease on a large scale of screening and to examine the usefulness of transvaginal ultrasonography (TVS) for endometrial disease screening in asymptomatic postmenopausal Japanese women. Methods: The study involved 1,400 postmenopausal women in whom endometrial thickness was measured with TVS, and then compared with the histopathological diagnosis of endometrial specimens. Results: The prevalence of endometrial disease in asymptomatic and symptomatic cases was 2.3 and 21%. In symptomatic cases, at a cut-off limit of 3 mm for endometrial thickness, the sensitivity for detecting endometrial disease was 94%, specificity 70% and positive predictive value 46%. With an endometrial thickness ≤3 mm, the probability that endometrial disease would be overlooked was 0.025.In asymptomatic cases, the corresponding figures at a cut-off limit of 3 mm were 90, 84, 12% and 0.003. Conclusions: TVS does not appear to be an effective screening method in asymptomatic postmenopausal Japanese women because of the low prevalence of endometrial disease in this population. We recommend a normal cut-off level for endometrial thickness of 4 mm in symptomatic postmenopausal Japanese women.