Chromosome analyses with banding were performed on six patients with idiopathic acquired refractory sideroblastic anemia (IARSA). One patient was found to have an extra chromosome No. 8, but had a normal level of red cell glutathione reductase. Bone marrow chromosomes from the other patients showed a normal karyotype. 28 patients with IARSA, including our 6 patients, have had chromosomal analyses. Two consistent chromosomal abnormalities have been described: a + 8 in three patients and a 20q- in three others. Despite the presence of chromosomal abnormalities in about one half of the patients, no patient has yet developed acute myelogenous leukemia. Several have died of hemochromatosis. The presence of a chromosomal abnormality appears to have no influence on the early course of IARSA.