The sideroblastic anemias are a heterogeneous group of congenital and acquired hematological disorders whose morphological hallmark is the presence of ringed sideroblasts--bone marrow erythroid precursors containing pathologic iron deposits within mitochondria. Here, by positional cloning, we define a previously unknown form of autosomal recessive nonsyndromic congenital sideroblastic anemia, associated with mutations in the gene encoding the erythroid specific mitochondrial carrier family protein SLC25A38, and demonstrate that SLC25A38 is important for the biosynthesis of heme in eukaryotes.