A 15-year-old girl was admitted to the hospital because of petechiae and was diagnosed with BCP-ALL. At the onset of the ALL, the BM sample revealed a female karyotype 46, XX, and FISH analysis for ETV/RUNX1 was not performed. Chemotherapy was started according to the Japan Adult Leukemia Study Group B-ALL213 protocol. The patient achieved CR after induction chemotherapy. Although she had been clinically well for 36 months, leukocytopenia was detected during regular consultation 12 months after frontline chemotherapy. A diagnostic test revealed a WBC of 2.8 x 109/L and 90% lymphoid blast cells in the BM. G-banded chromosome analysis of the BM sample revealed a female karyotype 46, XX, and FISH analysis revealed no ETV/RUNX1 fusion signals and 5-10 signals for the RUNX1 probe in 83% of the analyzed nuclei (Figure 2). Central nervous system infiltration was not found. She was diagnosed with late isolated BM relapse of iAMP21-positive BCP-ALL and treated according to the ALL-REZ BFM 2002 regimen. MRD in BM after induction was negative. On week 19 of chemotherapy, she received a 4/6 antigen matched unrelated CBT. The myeloablative conditioning regimen consisted of 12-Gy TBI from days -8 to -5 (six fractions), intravenous etoposide 1800 mg/m2 at day -4, and intravenous cyclophosphamide 60 mg/kg/day from days -3 to -2. Tacrolimus and short-term methotrexate were used for GVHD prophylaxis. Neutrophil engrafted on day 19 post-CBT. BM examination post-CBT revealed CR with 100% donor-type hematopoiesis. Grade I acute GVHD involving the skin only was well controlled by adjustment of tacrolimus. She has been in good condition for the last 45 months following CBT.