A 9-year-old female received an allogeneic stem cell transplant (SCT) from an ABO-incompatible HLA-matched sibling for β-thalassemia major, without achieving a complete donor chimerism. Subsequently, the patient received five donor lymphocyte infusions, without increasing donor chimerism, and autologous SCT. Due to the persistent bone marrow aplasia, the patient received a second allogeneic SCT from the same donor without obtaining any engrafment. After the double transplant failure, we performed an unrelated transplant from a full-matched umbilical cord blood (UCBT) without administering any neither conditioning regimen nor GVHD prophylaxis. Forty days after UCBT, trilinear engraftment was documented. Surprisingly, the hematopoietic reconstitution was related to the re-expansion of the autologous (beta-thalassemic) hematopoietic stem cell, as documented by chimerism studies. At present, 30 months after UCBT, there is stable hematopoietic autologous reconstitution. This is the first description of the restoration of autologous hematopoiesis obtained with UCBT in a thalassemia-major patient after a double transplant failure.