We describe unusual cytogenetic findings in a 33-year-old male with blastic phase of Philadelphia chromosome (Ph)-positive chronic myeloid leukemia. In addition to the t(9;22)(q34;q11), which was detected in all metaphases, a t(11;19)(q23;p13.3) was also identified as an evolutional change in all 20 metaphases. Fluorescence in situ hybridization (FISH) analysis showed that fusion signals of the ABL/BCR probes were found in 95% of blastic cells. Southern blotting and FISH analysis also revealed involvement of the MLL gene on 11q23. Clinical course was aggressive and the patient responded poorly to therapy. These findings suggest an association between Ph and 11q23 with poor prognosis, and that t(11;19)(q23;p13.3) was the essential pathogenic factor in our case.