Therapy-related myelodysplastic syndrome and acute myelogenous leukemia are increasingly being recognized as treatment complications in patients receiving chemotherapy or radiotherapy for previous neoplasms. However, therapy-related chronic myelogenous leukemia is relatively rare. A 61-year-old woman with a history of radiation therapy for breast cancer had previously, in 2007, received 4 courses of chemotherapy (RFM: rituximab, fludarabine, and mitoxantrone) for follicular lymphoma. In 2010, she was diagnosed with chronic-phase chronic myelogenous leukemia (CML) with Philadelphia chromosome but no other cytogenetic anomalies. Although a complete cytogenetic response (CCyR) was achieved with imatinib therapy, she developed leukocytosis with lymphoblasts and lymphoid crisis was diagnosed in January 2013. G-banded karyotyping showed 45, XX, -7, t, (9;22)(q33;q11.2). Unrelated bone marrow stem cell transplantation was performed after she had achieved a CCyR with dasatinib therapy. Polymerase chain reaction detected no major bcr/abl transcript in her bone marrow 42 days after transplantation. The majority of secondary leukemias resulting from the use of cytotoxic drugs can be divided into two well-defined groups depending on whether the patient has received alkylating agents or topoisomerase II inhibitors. However, concerns regarding the leukemogenic potential of fludarabine-based chemotherapy are growing. The potential risk of therapy-related leukemias including CML needs to be considered following fludarabine-based chemotherapy.