A three-year-old girl with chronic myelogenous leukemia (CML) experienced a pathological fracture of her femur after a demonstrated osteolytic bone lesion. Extramedullary disease (EMD) was diagnosed following the histologic findings of a biopsy of the osteolytic lesion. Frank blast crisis in the bone marrow followed one month later. This was the youngest patient to have been reported in English literature of Philadelphia chromosome positive (Ph+) CML with isolated bony EMD and pathological fracture. Treatment with a tyrosine kinase inhibitor, imatinib mesylate (Gleevec), in bone marrow accelerated phase of CML was failed to reverse the progression of blastic transformation, neither in the extramedullary bone lesion nor in the bone marrow.