Abstract: The present invention relates compositions and methods for microRNA expression profiling of cancer stem cells. In particular, the invention relates to a method for identifying and/or diagnosing one or more cancer stem cells, the method comprising identifying from a plurality of nucleic acid molecules, each encoding a microRNA sequence, one or more nucleic acid molecules are differentially expressed in the cancer stem cells and in one or more control cells, wherein the one or more differentially expressed nucleic acid molecules together represent a nucleic acid expression signature that is indicative for the presence of cancer stem cells. The invention further relates to a corresponding diagnostic kit of molecular markers, namely the nucleic acid expression signature. Finally, the invention is directed to a method using such nucleic acid expression signatures for preventing the proliferation and/or self-renewal of such cancer stem cells as well as to a corresponding pharmaceutical composition.