We describe a rare case of myelodysplastic syndrome that developed chronic myelogeneous leukemia with acquisition of Philadelphia chromosome. The major BCR/ABL transcript was confirmed by molecular analysis. Shortly thereafter, the patient showed transformation to blastic crisis. Hematological remission was achieved after 3 months of treatment with imatinib mesylate. The patient relapsed with additional chromosomal abnormalities and the disease became refractory to the treatment. Acquisition of the Philadelphia chromosome is an infrequent event in myelodysplastic syndrome, and the addition of this change to the initial genetic abnormality that caused MDS may have been associated with the accelerated clinical course of this patient.