The aim of this retrospective study was to detect endometrial lesions in tamoxifen breast cancer users (menopausal state related). The meaning of genital bleeding during the treatment and the actual incidence of benign and malignant pathology of the endometrium related to length of treatment was also evaluated. Tamoxifen (TMX) is a nonsteroidal triphenylene derivate with clear antiestrogenic properties on the breast which is used as adjuvant treatment for breast cancer; potential adverse effects include endometrial lesions. Three hundred and sixty-six breast cancer patients were enrolled in this study; 292 patients were treated with 20 mg/daily of TMX as adjuvant therapy and the remaining 74 did not receive therapy. All patients were subdivided in premenopausal and postmenopausal, asymptomatic and symptomatic groups All patients underwent ultrasound scans (to examine endometrial thickness) and hysteroscopic examinations before treatment and after one, three and five years. Endometrial biopsy under direct hysteroscopic vision was systematically performed. The pathological histology reports were classified under polyps, simple hyperplasia, complex hyperplasia, atypical hyperplasia, and carcinoma. A higher incidence of endometrial pathology was found only in symptomatic postmenopausal TMX treated patients (27.2% vs 19.5%) between the third and fifth year of treatment.