A 56-year-old female, who was diagnosed as CML in 1983 and had been well controlled with busulfan, was admitted to our hospital because of fever and iliac bone pain. Peripheral blood showed leukocytosis (WBC 70,000/microliters and bone marrow was normocellular with 53% leukemic cells, suggesting that she was in the blastic crisis. Chromosomal analysis of bone marrow cells at that time revealed t (9; 22; 12) and some additional abnormalities. The number of chromosomes ranged from 44 to 131 and the mode of chromosome number was 65. She was treated with combination regimen consisting of vincristine, 6-mercaptopurine and prednisolone and right iliac tumor was irradiated. Three months after admission, she died of DIC and pulmonary insufficiency due to leukemic infiltration.