BACKGROUND: Common complications after hematopoietic stem cell transplantation(HCT) include sepsis, graft versus host disease(GVHD), veno-occlusive disease(VOD), drug-induced nephrotoxicity, and acute renal failure(ARF). Prior studies report that the presence of ARF affects prognosis. However, we are unaware of such reports on the incidence of ARF after HCT in Koreans, and whether or not the development of ARF is related to prognosis. The purpose of our study was to investigate the cause of ARF after HCT and its relation to prognosis. METHODS: 163 patients received HCT at Seoul National University Hospital since 1985, of which, 107 were available for review. RESULTS: ARF after HCT developed in 52 patients (48.6%). In the three clinical causes, VOD, sepsis, and GVHD, risk factor related to the development of ARF was preexisting VOD. Logistic regression confirmed this association(odds ratio 4.4). The causes of ARF were different according to the periods it developed, and cyclosporin nephrotoxicity was the main cause through the whole period after HCT. The overall survival was worse in the ARF group(60 vs 73 %; p < 0.05). ARF group was split into two groups : patients whose peak serum creatinine levels were below 3.0 mg/dL(mild ARF group) and those who were above 3.0 mg/dL(severe ARF group). Severe ARF group had worse survival than mild ARF group and patients without ARF(p < 0.01). CONCLUSION: VOD, sepsis, GVHD after HCT increase the risk of the deveolopment of ARF, but cyclosprin nephrotoxicity is the main cause of ARF. Severe ARF is a factor influencing the prognosis of patients who received HCT.