A t(8;21)(q22;q22) without blood and bone marrow invasion by immature myeloid precursor cells occurred in a patient previously treated for polycythemia vera. The presence of a molecular rearrangement confirmed that the chromosomal abnormality was identical to that observed in acute leukemia with t(8;21). This case shows that the translocation, t(8;21), may occur in myelodysplasia and suggests that it can precede the appearance of overt leukemia.