Among various endometrial adenocarcinomas, endometrioid carcinoma can be very difficult to separate from serous carcinomas. Various biomarkers have been studied with proven value, including p53, Ki-67, and p16. In this study, we present data on another biomarker, IMP2, which we believe is sensitive and specific. Using 320 endometrial biopsy cases, we demonstrate that IMP2 is normally expressed in all proliferative and inactive endometrial glandular cells. The pattern of such expression is unchanged in serous carcinomas. IMP2 expression is, however, lost in all cases of endometrioid carcinomas by at least 25% to >95% of tumor cell populations. Therefore, loss of IMP2 expression can differentiate endometrioid from serous carcinomas. Such finding of IMP2 expression remained the same in mixed endometrioid and serous carcinomas; IMP2 expression is lost in all endometrioid components by at least 25% of tumor cell population, whereas it remained diffuse and strong in all serous components of carcinomas.