The primary aim of our study was to investigate the incidence of endometrial pathologies, especially endometrial cancer, in women with breast cancer treated with tamoxifen (TAM), aromatase inhibitors (AIs), or receiving no treatment (NT). The secondary aim was to identify, in this cohort, ultrasonographic findings that represent robust indications for hysteroscopy and endometrial biopsy, to avoid unnecessary second-level diagnostic procedures. Multicenter retrospective cohort study (Clinical Trial ID: NCT03898947). Data were collected from different Italian centers: Regina Elena National Cancer Institute of Rome, Arbor Vitae Centre of Rome, Gaetano Martino University Hospital of Messina, and Villa Sofia-Cervello Hospital of Palermo. We selected and consecutively included patients with a history of breast cancer who had undergone hysteroscopy for ultrasonographic or clinical indications between January 2007 and December 2016. Diagnostic hysteroscopy with endometrial biopsy or operative hysteroscopy, when clinically indicated. A higher percentage of patients in the TAM and AI groups had a normal endometrium compared with those in the NT group, whereas the incidence of endometrial polyps was higher in the NT group than in the others; no significant differences were observed among the 3 groups for other benign conditions or for premalignant and malignant uterine diseases, such as endometrial atypical hyperplasia and adenocarcinoma. TAM treatment does not seem to be associated with a higher rate of endometrial cancer in women with breast cancer compared with women treated with AIs or NT.