Cancer stem cells are defined as the unique subpopulation in the tumors that possess the ability to initiate tumor growth and sustain self-renewal as well as metastatic potential. Accumulating evidence in recent years strongly indicate the existence of cancer stem cells in solid tumors of a wide variety of organs. In this review, we will discuss the possible existence of a gastric cancer stem cell. Our recent data suggest that a subpopulation with a defined marker shows spheroid colony formation in serum-free media in vitro, as well as tumorigenic ability in immunodeficient mice in vivo. We will also discuss the possible origins of the gastric cancer stem cell from an organ-specific stem cell versus a recently recognized new candidate bone marrow-derived cell (BMDC). We have previously shown that BMDC contributed to malignant epithelial cells in the mouse model of Helicobacter-associated gastric cancer. On the basis of these findings from animal model, we propose that a similar phenomenon may also occur in human cancer biology, particularly in the cancer origin of other inflammation-associated cancers. The expanding research field of cancer stem-cell biology may offer a novel clinical apparatus to the diagnosis and treatment of cancer.