Serous (type 2) endometrial carcinomas are uniformly high grade, estrogen independent, often found in thin, atrophic endometria. This contrasts to the thickened endometrial stripe seen with endometrioid (type 1) carcinomas. In further distinction from type 1 carcinomas, type 2 carcinomas are known to metastasize widely without apparent myometrial invasion and without an identifiable stromal response—hence the difficulty in classifying a lesion as truly “intraepithelial” without data concerning its absence from usual sites of tumor metastasis. Endometrial intraepithelial carcinoma can be diagnosed cytologically by the findings of: marked nuclear atypia with enlarged nucleoli; confluent, strong p53 nuclear reactivity; and a marked increase in Ki-67 reactive nuclei. The very high Ki-67 proliferation index of these lesions exposes neoplastic epithelium that contrasts with surrounding atrophic epithelium. The p53 labeling is uniformly intense and confluent among malignant nuclei, unlike characteristically weak, spotty, or absent p53 labeling of early type 1 carcinoma and atypical hyperplasia.