Various endometrial lesions were more frequent among asymptomatic postmenopausal breast cancer patients who were treated with tamoxifen for > 48 consecutive months (30.8%) when compared with similar patients who were treated for 6-24 months or for 25-48 months (20.8% and 12.5%, respectively). However, this difference was not statistically significant. There were also no significant differences in the frequency of the various endometrial lesions between these three groups, although endometrial polyps were more frequently found among those treated for > 48 months. Overall, 20.7% of the 164 tamoxifen-treated patients in the study had an endometrial pathology. It can be concluded that there is a slight tendency among those postmenopausal patients who have been treated for > 48 consecutive months to have a higher frequency of endometrial lesions.