Failure to engraft donor cells is a devastating complication after allogeneic hematopoietic cell transplantation (HCT). We describe the results of 122 patients reported to the National Marrow Donor Program between 1990 and 2005, who received a second unrelated donor HCT after failing to achieve an absolute neutrophil count of >or=500/microL without recurrent disease. Patients were transplanted for leukemia (n = 83), myelodysplastic disorders (n = 16), severe aplastic anemia (n = 20), and other diseases (n = 3). The median age was 29 years. Twenty-four patients received second grafts from a different unrelated donor. Among 98 patients who received a second graft from the same donor, 28 received products that were previously collected and cryopreserved for the first transplantation. One-year overall survival (OS) after second transplant was 11%, with 10 patients alive at last follow-up. We observed no differences between patients who received grafts from the same or different donors, or in those who received fresh or cryopreserved product. The outcomes after a second allogeneic HCT for primary graft failure are dismal. Identifying risk factors for primary graft failure can decrease the incidence of this complication. Further studies are needed to test whether early recognition and hastened procurement of alternative grafts can improve transplant outcomes for primary graft failure.