ach year, approximately 50,000 patients worldwide undergo hematopoietic-cell transplantation. This procedure, which is used to treat a wide range of malignant and nonmalignant diseases, may involve either a myeloablative or reduced-intensity conditioning regimen; the use of alternative allogeneic donors (i.e., haploidentical or mismatched donors); cells from bone marrow, cord blood, or peripheral-blood stem cells; and new immunomodulatory agents to prevent graft-versus-host disease (GVHD) 1 (Table 1). Despite the overall improvement in outcomes after hematopoietic-cell transplantation, kidney injury remains a frequent complication and contributes to the morbidity and mortality associated with the procedure. 2-11 The onset of acute kidney injury and chronic kidney disease, which affect from 10 to 70% of transplant recipients, 2,7,12,13 varies from days after transplantation to months or years afterward. Acute injury is generally indicated by elevated levels of serum creatinine up to 100 days after transplantation, and chronic injury by elevated levels at or after 100 days. Acute kidney injury that persists for 3 months or longer is usually reclassified as chronic kidney disease. The overall health of the patient at the time of transplantation is generally assessed with use of a hematopoietic-cell transplantation-specific comorbidity index that includes the serum creatinine level. 14 In this index, which includes 17 categories of organ dysfunction, scores for organ-specific coexisting conditions range from 0 to 3, with higher scores indicating a greater severity of the condition. The risk categories are not fixed and can vary according to conditioning regimens. Scores on the comorbidity index range from 0 to 12. Higher scores on the index (the weighted sum of all the scores for organ-specific conditions and other pretransplantation characteristics) indicate a greater risk of death that is not associated with relapse. In general, patients with a score of 0 are considered to be at low risk of death that is not associated with relapse, those with a score of 1 or 2 are considered to be at intermediate risk, and those with a score of 3 or greater are considered to be at high risk. A score of 1 or more is correlated with a risk of acute post-transplantation kidney injury. 3 Such kidney injury may be caused by conditioning chemotherapy, total-body irradiation, nephrotoxic agents, infections, the hepatic sinusoidal obstruction syndrome (previously called veno-occlusive disease of the liver), transplantation-associated thrombotic microangiopathy, and GVHD. 3-7,15-19 This article reviews the causes, diagnosis, and management of complications and disorders of the kidney after hematopoietic-cell transplantation. Definition a nd Epidemiol ogy of K idne y Injur y Acute kidney injury after transplantation was initially defined as a doubling of the baseline serum creatinine level within the first 100 days after transplantation.