Genetically haploidentical stem cell transplants have been performed for several decades, mostly for patients with advanced acute leukemia. Such transplants are an option for those patients who do not have a histocompatible sibling donor. The historical data have been disappointing due to graft-versus-host disease, engraftment failure and delayed immune reconstitution. Recent modifications and new technological developments have led to more encouraging clinical results. Haploidentical transplantation is immediately available to the majority of patients with acute leukemia and is an acceptable alternative to matched unrelated donor transplantation.