The cancer stem cell hypothesis predicts that only a subpopulation of cells within a tumor is responsible for driving growth. If this hypothesis were true, it would have a significant impact on our current treatment of cancer because conventional chemotherapy and radiotherapy target rapidly proliferating cells making up the bulk of the tumor, not specifically cancer stem cells. The aims of this review are to highlight the current evidence supporting the existence of cancer stem cells in colorectal cancer, to consider the relative merits of current cancer stem cell markers, and to discuss the implications of this on our current treatment of cancer.Published scientific articles were selected by searching the PubMed database by use of the terms "colorectal," "cancer," and "stem cells," and by use of the bibliographies of extracted articles.CD133, a glycosylated cell surface protein, has been demonstrated to isolate for a subpopulation of colorectal tumor cells enriched in cancer stem cells. However, only 1 in 262 CD133+ cells are able to initiate tumors. Other cancer stem cell markers have been investigated, but an overall need exists to identify more specific markers to allow further characterization of these cancer stem cells. We discuss how increased understanding of the distribution and behavior of cancer stem cells within tumors could have significant implications for the management of colorectal cancer, including screening, resection margins, sentinel node biopsy, determination of prognosis, and the development of novel therapeutic targets.