Image cytometric DNA ploidy analysis of endometrial carcinomas was performed to determine whether ploidy status and ploidy-related parameters like DNA index, percentage of cells exceeding 5c and 9c, correlate with histologic subtype. This is a prospective study of 391 patients with stage I endometrial carcinoma which included 331 (85%) endometrioid adenocarcinoma, 22 (6%) serous adenocarcinoma, 7 (2%) clear cell adenocarcinoma, 2 (0.5%) small cell carcinoma, 1 (0.3%) undifferentiated carcinoma, and 28 (7%) unclassifiable adenocarcinoma. Twenty-five percent of endometrioid adenocarcinomas were non-diploid. In contrast, all clear cell adenocarcinomas and 21/22 (95%) of serous adenocarcinomas were non-diploid. Hyperdiploidy (25 cases) was found only in endometrioid adenocarcinomas. Mean DNA index of the stemline in serous adenocarcinoma (1.72) and clear cell adenocarcinoma (1.81) was higher than in endometrioid adenocarcinoma (1.1). The difference in ploidy-related parameters between endometrioid adenocarcinoma and serous adenocarcinoma was highly significant (P<0.001). In addition, Grade 3 endometrioid adenocarcinoma showed significant difference in all ploidy-related parameters compared with grade 1 and grade 2 tumors (P<0.001). Our results show that DNA ploidy-related parameters may be valuable in subtyping histologically difficult cases of endometrial carcinomas.