We describe a novel case of simultaneous karyotypic abnormalities of isochromosome 17q and trisomy 14 in a patient with myelodysplastic syndrome (MDS) in leukemic transformation. A 66-yr-old Korean man was admitted to Severance Hospital for evaluation of pancytopenia. On the basis of bone marrow studies at 3 different stages, he was diagnosed with MDS in leukemic transformation. Chromosome karyotyping repeatedly showed the same main clonal abnormalities, including isochromosome 17q and trisomy 14. Isochromosome 17q and trisomy 14 have each been reported as rare, nonrandom recurrent chromosomal abnormalities in patients with MDS showing a poor prognosis. To our knowledge, this is the first report of concurrent i(17)(q10) and trisomy 14 in a patient with MDS in leukemic transformation.