A case of a leukemic transformation following a 27-year history of idiopathic myelofibrosis (IMF) is presented. The patient had two chromosomal abnormalities: a deletion of chromosome 13, del 13(q12q14), and a deletion of chromosome 11, del 11(q14q23). This patient's final diagnosis was acute micromegakaryocytic leukemia, and she died 1 month after leukemic transformation with an additional chromosomal abnormality, trisomy 8. IMF with myeloid metaplasia associated with deletion of the long arms of chromosomes 11 and 13 has not been previously reported. We speculate that the leukemic transformation in this patient was associated with chromosomal abnormalities del 11 and trisomy 8. Am. J. Hematol. 78:67–70, 2005. © 2004 Wiley-Liss, Inc.