Most endometrial carcinomas contain only 1 Müllerian cell type although the presence of 2 or more cell types within 1 tumor, for example a predominantly low-grade endometrioid carcinoma with a minor component (arbitrarily defined as 30% or less) of high-grade serous and/or clear cell carcinoma, is not uncommon. The current study attempts to evaluate whether the presence of minor serous or clear cell components exerts an adverse effect on the prognosis in stage-I endometrial carcinomas of ''mixed-type.'' The study cases include 22 cases of stage-I endometrioid carcinoma with a minor component of serous carcinoma and 14 cases of endometrioid carcinoma with a minor component of clear cell carcinoma. Minor components were arbitrarily defined as representing anywhere between 5% and 30% of the total tumor. The study cases were compared with 56 cases of histologically pure age-matched and stage-matched endometrioid carcinomas, 6 pure serous carcinomas, and 13 pure clear cell carcinomas. All study and control cases were fully staged. Treatment history and outcome status were obtained and follow-up ranged from 56 to 140 months. Our study suggests that the presence of minor components of serous and clear cell carcinoma, defined as between 5% and 30%, within a mixed-type endometrial carcinoma appears to adversely influence the long-term survival of stage-I tumors, although a larger study is needed to corroborate our findings.