A 16-year-old girl developed a pain and paresis in the right hip joint in April 1994. Abdominal CT scan revealed hepatosplenomegaly and large tumor mass (6 x 7 x 13 cm) invading the right psoas muscle in the pelvic cavity. Laboratory data disclosed marked granulocytosis, the presence of Ph1 translocation and bcr-abl rearrangement, thus a diagnosis of CML was made. The tumor was shown to be consisted of granulocytes at all stages of development by a fine needle aspiration cytology. According to the criteria of IBMTR, the disease was classified as accelerated phase solely because the sum of myeloblasts and promyelocytes exceeded over 20%. The patient was treated with hydroxycarbamide, 6MP and dexamethasone, and marked reduction of the tumor mass was observed. Then an allogeneic BMT was performed from her HLA- identical brother on August 1994. She did not develop clinically significant symptoms except for grade I skin GVHD. The tumor was completely disappeared after the BMT as assessed by the abdominal CT scan. No cytological and chromosomal relapse has been observed for 20 months after the BMT.