Surface epithelial changes involving endometrioid carcinomas of the uterine corpus mimicking papillary syncytial metaplasia or cervical microglandular hyperplasia are relatively common. There have been rare reports of surface epithelial changes in endometrioid carcinomas mimicking ovarian serous borderline tumor or low-grade serous carcinoma. We report an endometrioid carcinoma of the uterine corpus with striking morphologic mimicking of an ovarian serous borderline tumor with only a minimal amount of conventional endometrioid carcinoma. The tumor was diffusely positive for estrogen receptor, negative for WT1, and showed wild-type immunoreactivity with p53. Targeted sequencing revealed a KRAS mutation (G12V/D/A), but no BRAF mutation. This close mimicry of a serous borderline tumor by a uterine endometrioid carcinoma has not been emphasized in the literature and this case is unique because the features involved almost the entire neoplasm. In reporting this case, we review surface changes in endometrioid carcinomas of the uterine corpus.