Abstract Uterine cancer is the fourthmost common cancer in the UK. Transvaginal ultrasound (TVS) provides a reliable means of determining endometrial thickness. There is little consensus as to the optimum endometrial thickness threshold for investigation of endometrial cancer. The aim of our study was to ascertain an appropriate endometrial thickness (ET) while limiting unnecessary investigation. A prospective study of women with postmenopausal bleeding (PMB) referred to the rapid access clinic over a 2-year period was undertaken. The primary investigation was TVS and if the ETwas≥4mm,
an endometrial sampling (Pipelle®) or a hysteroscopy was undertaken. Endometrial cancers were identified from the pa-thology reporting system and a search of the Northern and Yorkshire Cancer Registry Information Service (NYCRIS). Pre-test/post-test risks of endometrial cancer and numbers needed to test were calculated to determine optimum ET
threshold. There were 1045 referrals to the rapid access clinic with a history of PMB. Pre-test risk of endometrial cancer was 6.5 %. Post-test risk was stratified according to ET measure-ment. The probability of an endometrial cancer at anET < 4 mm was 0.3 %. Binary logistic regression analysis confirmed a statistically significant linear correlation between ET and the risk of developing endometrial cancer (p< 0.0001). The numbers needed to test in order to diagnose one case of endometrial cancer at 3 mm is 11 when compared with 4 at 10 mm. The authors conclude a threshold of ET≥4 mm ensures the majority of cancers are detected with minimal unnecessary invasive investigation.