There is now sufficient evidence to conclude that rare populations of epithelial stem/progenitor cells and MSC-like cells are present in human and mouse endometrium. While there is some evidence for the monoclonality of individual endometrial glands, it is still not clear whether epithelial stem/progenitor cells exist as single or multiple cells in the bases of individual glands. There is much interest in the hypothesis that foci of endometriosis which are monoclonal in origin are initiated by retrogradely shed endometrial stem/progenitor cells and their niche cells in women who develop endometriosis. Genealogy studies on menstruated fragments, the recent evidence for the presence of MSC-like cells in menstrual blood, and the identification of markers that enables the prospective isolation and identification of endometrial MSC-like cells provides impetus for investigating the role of endometrial stem/progenitor cells in the pathogenesis of endometriosis. The eventual goal would be to target self-renewal processes in shed endometrial stem/progenitor cells as novel therapeutic options for the treatment of endometriosis.