Sixteen patients who underwent a second allogeneic hematopoietic stem cell transplantation (HSCT2) for leukemia relapse after the first allogeneic transplantation (HSCT1) were studied. The patients included 7 patients with acute myelogenous leukemia, 8 with acute lymphoblastic leukemia, and 1 with chronic myelogenous leukemia. The median patient age at HSCT2 was 22 years (range, 12 to 44 years). The median interval between HSCT1 and HSCT2 was 19 months (range, 2 to 46 months). At HSCT2, 7 patients were in complete remission (CR), 7 had relapsed, and 2 had bone marrow aplasia. In 14 patients, donors for HSCT2 were the same as those for HSCT1. Two donors were replaced, 1 for another HLA-matched sibling and 1 for an unrelated cord blood donor. Four patients (25%) died within 100 days after HSCT2 from veno-occlusive disease, sepsis, interstitial pneumonitis, or chronic graft-versus-host disease (GVHD), without leukemia relapse. Seven patients (44%) developed leukemia relapse and died between 4 and 20 months after HSCT2. Five patients (31%) survived beyond 4 years. One patient died from chronic GVHD without leukemia relapse 55 months after HSCT2. The 4 other patients were alive between 79 and 134 months after HSCT2 (median follow-up, 106 months). Factors that favorably influenced survival were age younger than 20 years and CR duration after HSCT1 longer than 12 months. HSCT2 is considered to be beneficial for select patients. Preparative regimens, GVHD prophylaxis, and donor choice for HSCT2 need to be studied to obtain a more successful outcome for HSCT2.