We report a retrospective analysis of acute renal failure (ARF) in a group of 54 adult patients with hematological malignancies treated with unrelated cord blood transplantation (CBT) after myeloablative conditioning. All patients received four fractionated 12 Gy total body irradiation and chemotherapy as myeloablative conditioning. ARF was defined as the doubling serum creatinine occurring within the first 100 days after CBT. A statistically significant decrement of renal function from baseline was observed in days between 11 and 20. ARF occurred in 27.8% of patients. Although no difference was seen in maximum cyclosporine trough levels, the maximum of vancomycin (VCM) trough levels were significantly higher in patients with ARF (p = 0.01). Our result suggests that it is important to monitor VCM dosing more strictly with pharmacokinetic assessment, especially in days 11 - 20, when the most frequently observed declining renal function.