Objective: The recent characterization of possible stem/progenitor cells in the endometrium has shed new light on the origins of ectopic endometrial tissue and the mechanism for the pathogenesis of endometriosis, but has raised new questions. Is it possible that abnormal endometrial stem/progenitor cells increase their capacity to implant and establish themselves as ectopic tissue, or that normal stem cells implant in abnormal peritoneum? This study investigated key stem cell properties in cologenic epithelial and stromal cells obtained from eutopic endometrium of women with endometriosis. Study design: Single cell suspensions of endometrial epithelial and stromal cells were cultured at densities of 20, 50, 100 and 200 cells/cm(2). Cloning efficiency (CE) was determined, and stem cell phenotypic surface markers were detected using Western blotting and quantitative real-time polymerase chain reaction. Results: CE was significantly higher in cells cultured at a density of 50 cells/cm(2) compared with the other groups. After 15 days of culture, small and large colonies were observed. Large-colony-derived epithelial and stromal cells had high proliferative potentials, producing millions of cells in vitro, with strong expression of epithelial and stromal stem cell phenotypic surface markers EMA, CK, CD49f, THY-I (CD90), collagen type I, 5B5 and vimentin. Conclusion: Adult stem cells were found in eutopic endometrium of women with endometriosis, and this may play an important role in disease development. (C) 2014 Elsevier Ireland Ltd. All rights reserved.