Centromere spreading (CS) was observed in bone marrow chromosomes from a patient with acute myeloblastic leukemia (AML), prior to therapy. The abnormality was found in a direct specimen, in a 24-hr culture, and in a culture treated with the methotrexate synchronization technique. A small hypodiploid clone, 45,XY,-19, was also observed. This case provides further evidence that CS can occur in acute nonlymphocytic leukemia (ANLL). The possible relationship between CS and hypodiploidy in this and other reported cases of ANLL is discussed.