Poorly differentiated endometrial carcinomas of specific type include the rarely reported endometrial carcinoma with a malignant giant cell component [endometrial giant cell carcinoma (GCC)]. Since the initial description in 1991, there has only been 1 subsequent case report of this entity. We report another 5 cases. The patients ranged in age from 53 to 83 years, presenting with vaginal bleeding, anemia, or a pelvic mass. Four of the 5 tumors contained areas of endometrial adenocarcinoma of usual type, with a variable giant cell component. The conventional cell types present included 1 case with clear cell carcinoma (30% of tumor volume), 2 with high-grade endometrioid carcinoma (50% and 70% of tumor volume, respectively) and 1 with serous histology (10% of tumor volume). One was composed exclusively of giant cell carcinoma. The giant cell component in all cases consisted of poorly cohesive nests of bizarre multinucleated giant cells with mononuclear tumor cells. A striking peritumoral and intratumoral inflammatory cell infiltrate composed of lymphocytes, plasma cells and focal eosinophils, and neutrophils was present and emperipolesis was noted in 4 of the 5 cases. The giant cells showed focal staining for epithelial markers (AE1/AE3 and CAM 5.2). Three of the patients presented with stage 1A disease, 1 with stage 1B disease, and 1 tumor was advanced, presenting as stage IIIC2. One patient in whom the tumor was exclusively of the giant cell type, developed lung metastasis 4 years after diagnosis and 1 patient is disease free after 14 years. The remaining 3 patients showed no evidence of disease with 15 to 32 months of follow-up. As histotype supplemented by staging information is critical in selection of treatment modalities and in prognostication in uterine malignancies, accurate classification is mandated. Here, we present a series of endometrial carcinomas containing a component of GCC and discuss the spectrum of giant cell-containing uterine neoplasms. At this time, however, the cumulative data on endometrial GCC are limited and the prognostic significance of the presence and the extent of a giant cell component in endometrial carcinoma remains uncertain.