Twenty-four children with acute leukemia (21) or chronic myeloid leukemia (3) who relapsed after a first hematopoietic stem cell transplantation (HSCT) underwent a second allogeneic HSCT. Sixteen patients died from relapse or transplant related causes and 8 are alive and disease-free with a probability of event-free survival at 5 years of 32%. These results show that this procedure offers a chance to a subset of these patients.