We report a patient with PML/RARalpha-positive acute promyelocytic leukemia (APL) who developed PML/RARalpha-negative acute myeloid leukemia 37 months after allogeneic bone marrow (BMT) transplant for molecular relapse. Features of myelodysplasia were noted 11 months earlier, chimerism testing by analysis of short tandem repeats was consistent with development of myelodysplasia and acute leukemia within cells of donor origin. To our knowledge, this is the first report of donor cell leukemia following BMT for APL. We hypothesize that replicative stress may lead to the development of some cases of donor cell acute leukemia.