Objective. The aim of this study is to estimate the prevalence of endometrial pathology before the start of tamoxifen therapy in menopausal breast cancer patients. Methods. Ninety- one gynecologically asymptomatic patients, suffering from estrogen receptor- positive breast cancer and scheduled for adjuvant tamoxifen, underwent pretreatment endometrial assessment. In all patients, a transvaginal ultrasonography was carried out; a double- layered endometrial stripe measuring above 4 mm was considered as abnormal. In these patients, outpatient hysteroscopy and endometrial biopsy were performed. Pathologic findings were considered the reference test in estimating the prevalence of endometrial morbidity. Results. In 34 patients (37.3% ) a thickened endometrium was an indication for hysteroscopic and pathologic assessment. Endometrial polyps, simple hyperplasias, and complex atypical hyperplasias were found in 10 (10.9% ), 4 (4.3% ), and 3 (3.2% ) patients, respectively, leading to an overall prevalence of baseline endometrial morbidity of 18.6% . Established individual risk factors for development of endometrial pathology, such as body mass index, age at menarche and menopause, and parity, did not significantly differ in patients with and without endometrial abnormalities. Only patients’ age (63.8 ± 8.6 and 52.2 ± 11.8; P = 0.03) and endometrial thickness (10.5 ± .3.5 and 3.9 ± .3.0;P >0.001) were significant predictive factors of endometrial pathology. Conclusions. Menopausal women with estrogen receptor- positive breast cancer appear to have high risk of baseline subclinical endometrial abnormalities; therefore, an endometrial assessment, before the start of tamoxifen therapy, is always recommended in such patients. Objective. The aim of this study is to estimate the prevalence of endometrial pathology before the start of tamoxifen therapy in menopausal breast cancer patients. Methods. Ninety-one gynecologically asymptomatic patients, suffering from estrogen receptor- positive breast cancer and scheduled for adjuvant tamoxifen, underwent pretreatment endometrial assessment. In all patients, a transvaginal ultrasonography was carried out; a double- layered endometrial stripe measuring above 4 mm was considered as abnormal. Pathologic findings were considered the reference test In estimating the prevalence of endometrial morbidity. Results In 34 patients (37.3%) a thickened endometrium was an indication for hysteroscopic and pathologic assessment. Endometrial polyps, simple hyperplasias, and complex atypical hyperplasias were found in 10 (10.9%), 4 4.3%), and 3 (3.2%) patients, respectively, leading to an overal l prevalence of baseline endometrial morbidity of 18.6%. Established individual risk factors for development of endometrial pathology, such as body mass index, age at menarche and menopause, and parity, did not significantly differ in patients with and without endometrial abnormalities. Only patients’ were significantly predictive factors of endometrial pathology. Conclusions. Menopausal women with estrogen receptor-positive breast (63.8 ± 8.6 and 52.2 ± 11.8; P = 0.03) and endometrial thickness (10.5 ± 3.5 and 3.9 ± 3.0; cancer appear to have high risk of baseline subclinical endometrial abnormalities; therefore, an endometrial assessment, before the start of tamoxifen therapy, is always recommended in such patients.