We describe herein a case of bone marrow failure in a 53-year-old patient affected by Ph1-positive chronic myeloid leukemia who received an HLA-identical AB0-mismatched bone marrow transplant from a 56-year-old sibling donor. Hematopoietic recovery after marrow failure was obtained following two consecutive courses of rh-G-CSF-mobilized peripheral blood stem cell infusions. No potential risk factors associated with graft failure, excluding recipient and donor age, were documented, whereas a relatively high number of progenitor cells were necessary to overcome the host-versus-graft barrier in our patient. Therefore we suggest that growth factor-stimulated peripheral blood should be considered as the first choice for allogeneic stem cells in order to avoid primary graft failure with donors over 50 years of age.