T he R200W mutation in the von Hippel–Lindau (VHL) tumor suppressor protein (pVHL) is unique in that it is not associated with tumor development, but rather with Chuvash polycythemia, a heritable disease characterized by elevated hematocrit and increased serum levels of erythropoietin and VEGF. Previous studies have implicated hypoxia-inducible factor–1α (HIF-1α) signaling in this disorder, although the effects of this mutation on pVHL function are not fully understood. In order to explore the mechanisms underlying the development of this polycythemia, we generated mice homozygous for the R200W mutation (Vhl^R/R). Vhl^R/R mice developed polycythemia highly similar to the human disease. The activity of HIF proteins, specifically the HIF-2α isoform, was upregulated in ES cells and tissues from Vhl^R/R mice. Furthermore, we observed a striking phenotype in Vhl^R/R spleens, with greater numbers of erythroid progenitors and megakaryocytes and increased erythroid differentiation of Vhl^R/R splenic cells in vitro. These findings suggest that enhanced expression of key HIF-2α genes promotes splenic erythropoiesis, resulting in the development of polycythemia in Vhl^R/R mice. This mouse model is a faithful recapitulation of this VHL-associated syndrome and represents a useful tool for studying polycythemias and investigating potential therapeutics.