Since 1985, when Killackey originally described three cases of endometrial carcinoma in patients receiving tamoxifen, there have been several reports confirming or denying the relationship between tamoxifen and endometrial carcinoma. Our study of 15 patients treated for breast carcinoma with tamoxifen found that papillary serous carcinoma was the most common tumor in this group of patients. Several other retrospective studies reported a high incidence of high-grade endometrioid adenocarcinoma or high-risk variants of endometrial carcinoma in patients receiving tamoxifen.