We report on a patient with myelodysplastic syndrome (MDS) which resembled chronic myeloproliferative disorder (CMPD). A 67-year-old male was admitted to our hospital in June 1990. A diagnosis of refractory anemia with excess of blasts in transformation (RAEB-T) was based on the peripheral blood and bone marrow findings on admission. However, since thrombocytosis and bone marrow fibrosis was noted, the patient was diagnosed as MDS with myelofibrosis. Low-dose cytosine arabinoside therapy was performed. Although complete remission could not be achieved, a high quality of life could be maintained by appropriate transfusion. In January 1993, the patient was readmitted because of a marked increase in mature neutrophils, showing a moderate increase of blasts, chromosomal aberration (46,XY,12p-) and hepatosplenomegaly; but no fibrosis of bone marrow was observed. These findings suggested that neoplastic proliferation at the level more differentiated to granulocytic lineage occurred at the terminal stage and that his clinical feature was located between MDS and CMPD. This case may be important in considering various aspects of MDS.