Shwachman-Diamond syndrome (SDS) is an autosomal recessive disorder characterized by pancreatic insufficiency and variable degrees of neutropenia. SDS patients are at risk of developing myelodysplasia, aplastic anemia, and leukemic transformation. The role and timing of allogeneic hematopoietic stem cell transplantation (HSCT) in SDS remain controversial. We report three SDS patients with severe aplasia transplanted using unrelated umbilical cord blood (UCB). Patients received melphalan (180mg/m 2 ), etoposide (1200mg/m 2 ), anti-thymocyte globulin (90mg/kg), and total lymphoid irradiation (500cGy); graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporine and prednisone. Myeloid engraftment occurred promptly with absolute neutrophil count >500 cells/mm 3 on day 15±5 and all patients displayed 100% donor chimerism by 2 months post transplant. The major complication of transplant was GVHD, with all patients developing grade II or III acute GVHD, one progressing to chronic extensive GVHD. Patients are alive 309, 623, and 2029 days post transplant. Factors important in HSCT outcome for SDS may include transplantation at a young age, avoidance of cyclophosphamide, and adequate GVHD prophylaxis. Importantly, these cases also suggest that unrelated UCB, in the absence of a matched family member, is an excellent alternative stem cell source for SDS patients undergoing HSCT. © 2005 Nature Publishing Group All rights reserved.