SIRT1 is an NAD(+)-dependent histone deacetylase implicated in the establishment of the primitive hematopoietic system during mouse embryonic development. However, investigation of the role of SIRT1 in adult hematopoiesis has been complicated by the high perinatal mortality of SIRT1-deficient mice (SIRT1(-/-)). We performed a comprehensive in vivo study of the hematopoietic stem cell (HSC) compartment in adult SIRT1(-/-) mice and show that, apart from anemia and leukocytosis in older mice, the production of mature blood cells, lineage distribution within hematopoietic organs, and frequencies of the most primitive HSC populations are comparable to those of wild-type littermate controls. Furthermore, we show that SIRT1-deficient BM cells confer stable long-term reconstitution in competitive repopulation and serial transplantation experiments. The results of the present study rule out an essential physiologic role for cell-autonomous SIRT1 signaling in the maintenance of the adult HSC compartment in mice.