Hypoxia-induced signaling is important for normal and malignant hematopoiesis. The transcription factor hypoxia-inducible factor-1α (HIF-1α) plays a crucial role in quiescence and self-renewal of hematopoietic stem cells (HSCs) as well as leukemia-initiating cells (LICs) of acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). We have investigated the effect of HIF-1α loss on the phenotype and biology of FLT-3(ITD)-induced myeloproliferative neoplasm (MPN). Using transgenic mouse models, we show that deletion of HIF-1α leads to an enhanced MPN phenotype reflected by higher numbers of white blood cells, more severe splenomegaly and decreased survival. The proliferative effect of HIF-1α loss is cell-intrinsic as shown by transplantation into recipient mice. HSCs loss and organ specific changes in number and percentage of long-term hematopoietic stem cells (LT-HSCs) were the most pronounced effects on a cellular level after HIF-1α deletion. Furthermore, we found a metabolic hyperactivation of malignant cells in the spleen upon loss of HIF-1α. Some of our findings are in contrary to what has been previously described for the role of HIF-1α in other myeloid hematologic malignancies and question the potential of HIF-1α as a therapeutic target.Leukemia accepted article preview online, 24 June 2015. doi:10.1038/leu.2015.156.