The cancer stem cell (CSC) theory has been proposed to explain the tumor heterogeneity and carcinogenesis process. Recent studies indicate that aldehyde dehydrogenase (ALDH) activity represents a promising CSC marker. Here, we aimed to determine whether human adenoid cystic carcinoma (AdCC) also follows CSC model by exploring the CSC properties of AdCC cells expressing high level of ALDH activity. Utilizing in-vivo series transplantation assays, we found ALD(High) AdCC cells were capable of self-renewal and of generating tumors. that recapitulate the heterogeneity of the parental tumor. Utilizing in-vitro assay, we found only ALDH(high) AdCC cells have tumorsphere-forming ability in anchorage-independent cultures. Finally, we showed ALDH(high) AdCC cells possess highly invasive capability and are responsible for mediating metastasis. These findings suggest the existence of a developmental hierarchy within human AdCC and further elucidation of the unique survival mechanism of AdCC derived CSC population may provide novel therapeutic strategies to treat AdCC. (c) 2010 Elsevier Inc. All rights reserved.