Two monozygotic twins from a Swedish, nonconsanguine family-with concordant acute myeloid leukemia and similar morphological and cytogenetic changes, but with additional changes in one twin, suggestive of clonal evolution-are described. Twin I relapsed 4 months after completion of treatment, while twin II was still on treatment and was transplanted with stem cells from the human leukocyte antigen-identical father. An early relapse after transplantation was treated with donor lymphocyte infusions, but twin I relapsed again and died 8 months after stem cell transplantation (SCT). On relapse of twin I, treatment of twin II was reconsidered and consolidation was intensified with SCT in CR1 with peripheral blood stem cells from the father. Due to irreversible liver failure caused by severe venoocclusive disease, a living, related liver transplantation from the father was performed on day +84 post-SCT. Minimal immunosuppression was required, and graft rejection did not occur. The patient was in complete remission 29 months after SCT and 25 months after liver transplantation.