59 year old female was admitted to Nagoya Memorial Hospital for anemia unknown etiology after the work up of the gastrointestinal tract. Peripheral blood count at admission was as follows: WBC 2,400/microliters, RBC 321 X 10(4)/microliters, Hb 9.8 g/dl, Ht 30.1%, Plt 8.2 X 10(4)/microliters, which showed pancytopenia with normocytic, normochromic anemia. She had no hepatosplenomegaly, vitamin B12 nor folate deficiency. Bone marrow was hyperplastic and showed trilineage megalodysplastic changes. The diagnosis of myelodysplastic syndrome (Refractory anemia) was made. Progenitor assay showed no colony formation of BFU-E but showed normal growth of CFU-GM colony and cluster. She had chromosomal abnormality of 47, XX, + 11. Administrated anabolic steroid, prednine and activated vitamin D3 were not effective and she died of brain hemorrhage in April 1987. Colony assay at this stage showed numerous leukemic clusters and no normal colonies. Re-performed chromosome assay showed 47, XX, + 11. There are only a few reports of trisomy-11 in a patient with MDS. Especially we could follow this case till her leukemic transformation by colony assay.