A review of the pathology and cytopathology of 295 endometrial adenocarcinomas treated surgically at King Edward Memorial Hospital for Women, with full 5-year follow-up, revealed 16 cases of pure serous carcinoma (USC), 10 cases of mixed serous and endometrioid carcinoma with a predominant serous component (mixed USC-EAC) and six cases of mixed serous and endometrioid carcinoma with a predominant endometrioid component (mixed EAC-USC). The mixed carcinomas may be characterized microscopically by classical serous features side by side with classical endometrioid features, or additionally by features intermediate between the two. Many of these features are reproduced in preoperative cervicovaginal smears. USC and mixed USC-EAC were found to be indistinguishable clinically and prognostically, with an identical corrected 5-year survival of 40%, although numbers are small. Mixed EAC-USC (which contained 10–25% serous differentiation in this series), however, were similar in many respects to a control population of 95 EAC of Grade 2 and 3. The corrected 5-year survival in these two groups was 67% and 79%, respectively, which is not statistically significant in this small series. This study suggests that the behavior of a mixed tumor containing 50% or more serous differentiation is similar to that of pure serous carcinoma, and that the behavior of a mixed tumor containing less than 25% serous differentiation is similar to that of the other component. Given the poor correlation between pathologic findings in curettage and subsequent hysterectomy specimens, however, identification of any significant serous element in curettage material may prove vital in optimizing surgical and adjuvant therapy.