During the last 20 years, several concepts regarding the biology of acute myeloid leukemia (AML) have changed in a profound manner. This has been mainly due to significant advances in the identification, purification and characterization of the primitive hematopoietic cells--including stem and progenitor cells--in which this disorder originates. In the present review article, we discuss some of these new concepts and their relevance in the treatment of AML.