HLA disparity is a major risk factor for graft rejection and GVHD. We report a patient with CML (accelerated phase) who underwent allogeneic SCT from a mismatched unrelated donor and developed acute GVHD. With immunosuppression, GVHD symptoms improved but graft rejection occurred. After a second conditioning regimen, the patient received a second graft from a haploidentical related donor. Engraftment occurred, but the patient died from GVHD and pulmonary aspergillosis. Chimeric analysis revealed that all leukocytes were of donor 2 origin apart from CD3+ T cells, which were 100% donor 1 type. Thus, in spite of intensified immunosuppression and successful transplantation of a second graft, T cells from the first donor persisted and induced severe acute GVHD.