Sphingosine-1-phosphate (S1P), a sphingolipid metabolite that plays an important role in the regulation of cell survival, growth, migration, and angiogenesis acts both inside the cells and as an extracellular mediator through binding to five G protein-coupled receptors (S1P1-5). Sphingosine kinase 1 (SK1), the enzyme responsible for S1P production, is over-expressed in many solid tumors, including gliomas. One common feature of these tumors is the presence of “hypoxic regions”, characterized by cells expressing high levels of hypoxia-inducible factors HIF-1a and HIF-2a, two transcription regulators that modulate the levels of proteins with crucial roles in tumor progression. So far nothing is known about the role and the regulation of SK1 during tumor-induced hypoxia or about SK1 regulation and HIFs. Here we investigated the role of HIF-1a and HIF-2a in the regulation of SK1 during hypoxic stress in glioma-derived cells U87MG. We report that hypoxia increases SK1 mRNA levels, protein expression and enzyme activity, followed by intracellular S1P production and S1P release. Interestingly, knock-down of HIF-2a by siRNA abolished the induction of SK1 and the production of extracellular S1P after CoCl2 treatment, whereas HIF-1a siRNA resulted in an increase of HIF-2a and of SK1 protein levels. Moreover, using Chip analysis we demonstrate that HIF-2a binds the SK1 promoter. Functionally, we demonstrate that conditioned media from hypoxia-treated tumor cells results in neo-angiogenesis in human umbilical vein endothelial cells (HUVEC) in a S1P receptor-dependent manner. These studies provide evidence of a link between S1P production as a potent angiogenic agent and the hypoxic phenotype observed in many tumors.