Notch signaling pathway regulates many different events of embryonic and adult development: among them, Notch plays an essential role in the onset of hematopoietic stem cells and influences multiple maturation steps of developing lymphoid and myeloid cells. Deregulation of Notch signaling determines several human disorders, including cancer. In the last decade it became evident that Notch signaling plays pivotal roles in the onset and development of acute leukemia by regulating the intracellular molecular pathways involved in leukemia. Here, the data concerning acute leukemia and bone marrow stromal cells has been critically reviewed in light of the most recent findings on Notch signaling in stromal microenvironment.