The enzymes that belong to the aldehyde dehydrogenase family are expressed in a variety of cells; yet activity of their main members characterizes stem cells, both normal and malignant. Several members of this family perform critical functions in stem cells, in general, and a few have been shown to have key roles in malignant tumors and their recurrence. In particular, ALDH1A1, which localizes to the cytosol and the nucleus, is an enzyme critical in cancer stem cells. In acute myeloid leukemia (AML), ALDH1A1 protects leukemia-initiating cells from a number of antineoplastic agents, and proves vital for the establishment of human AML xenografts in mice. ALDH2, which is located in mitochondria, has a major role in alcohol metabolism by clearing ethanol-derived acetaldehyde. Haematopoietic stem cells require ALDH2 for protection against acetaldehyde, which can cause damage to DNA, leading to insertions, deletions, chromosomal rearrangements, and translocations. Mutations compromise stem cell function, and thereby threaten blood homeostasis. We review here the potential of targeting the enzymatic activity of aldehyde dehydrogenases in acute leukemia.