Indisputable advances in the conventional therapy of chronic myeloid leukemia (CML), like the establishment of interferon-alfa as the standard treatment for first chronic phase patients and the introduction of imatinib-mesylate as a highly active compound in patients failing interferon-alfa treatment or with more advanced disease are challenging allogeneic stem cell transplantation (SCT) as the single treatment modality, which currently offers long-term remissions below the threshold of sensitive molecular methods for the detection of BCR-ABL transcripts. Since stable molecular remissions are thought to be a prerequisite for cure of CML, allogeneic SCT remains the only curative treatment option for younger patients (i.e. beyond the age of 55 years), who have an HLA-matched related or unrelated donor. Nowadays, suitable HLA-matched unrelated donors can be identified for 70% to 75% of caucasian patients lacking an HLA-identical sibling donor, which substantially has promoted the broader application of allogeneic SCT.