Histological findings of endometrial specimens collected by hysteroscopy from 261 postmenopausal breast cancer patients with tamoxifen treatment (group I) and from endometrial specimens obtained following hysterectomy from 40 similar patients (group II) were compared. This comparison was performed in order to assess whether endometrial pathologies are more frequently diagnosed in specimens collected by hysterectomy than by those collected during hysteroscopy in such patients. Overall positive endometrial histological findings were significantly more common in group II patients than in group I patients (82.5 and 24.5%, respectively; p < 0.0001). Atrophic endometrium was significantly more common in group I patients than in group II patients (75.5 and 15.0%, respectively; p < 0.0001). All other different endometrial pathologies, except for proliferative endometrium, were significantly more common in group II patients than in group I patients (endometrial hyperplasia = 17.5 and 4.2%, respectively; p < 0.0003; endometrial polyps = 30.0 and 11. 5%, respectively; p < 0.006; endometrial polyps with hyperplasia = 17.5 and 4.2%, respectively; p < 0.0003; endometrial carcinoma = 15. 0 and 0.4%, respectively; p < 0.0001). These findings suggest that in postmenopausal breast cancer patients treated with tamoxifen, the frequency of various endometrial histological findings and of overall positive endometrial histological findings were significantly higher in specimens collected by hysterectomy than in specimens obtained by hysteroscopy.