Adult stem cells have recently been identified in several types of mature tissue and it has also been suggested that stem-like cells exist in cancerous tissues. In this regard, stem-like cell subpopulations, referred to as side-population (SP) cells, have been identified in several tissue and tumor types, based on their ability to remove intracellular Hoechst 33342, a fluorescent dye. We have isolated and characterized SP cells from normal human endometrium and an endometrial cancer cell line. Endometrial SP cells can function as progenitor cells. Endometrial cancer SP cells possess the following characteristics: i) reduced expression levels of differentiation markers, ii) long-term repopulating properties, iii) self-renewal capacity, iv) enhanced migration and podia formation, v) enhanced tumorigenicity, and vi) bi-potential development (tumor cells and stroma-like cells), suggesting that they have cancer stem-like cell features. Recently, we demonstrated that sodium butyrate, a histone deacetylase (HDAC) inhibitor, inhibited the self-renewal capacity of endometrial cancer SP cells by inducing a DNA damage response. Here, we review recent articles that show the presence of stem cells in normal endometrium and endometrial cancer and introduce the results of our own recent studies.