Acute kidney injury (AKI) has significant prognostic implications for long‐term outcomes in patients undergoing liver transplantation. In several retrospective studies, perioperative variables have been associated with AKI. These variables have been mainly associated with changes in creatinine concentrations over several days or months post‐transplantation. To better define AKI, new markers have become available that help to identify patients at risk for renal injury within hours of a triggering insult. We prospectively enrolled liver transplant patients at our institutions to evaluate neutrophil gelatinase‐associated lipocalin (NGAL), a marker of early renal injury, as a surrogate for AKI in patients undergoing liver transplantation. Blood was prospectively collected at predetermined time points from 59 patients at 2 institutions. The electronic anesthesia records and the hospital computer data system were reviewed for perioperative variables. Data collection included patient demographics, intraoperative variables such as fluid management, transfusion requirements, hemodynamics, and urine output. Subsequently, patients were grouped according to the presence of risk for developing AKI as defined by the RIFLE (risk, injury, failure, loss, and end‐stage kidney disease) criteria. The difference between the NGAL concentration 2 hours after reperfusion and the baseline NGAL concentration was predictive of AKI in all patients, including patients with preexisting renal dysfunction. In patients with creatinine concentrations less than 1.5 mg/dL, a single NGAL determination 2 hours after reperfusion of the liver was associated with the development of AKI. Total occlusion of the inferior vena cava was associated with AKI. In conclusion, NGAL concentrations obtained during surgery were highly associated with postoperative AKI in patients undergoing liver transplantation. These findings will allow the design of larger interventional studies. Our findings regarding the impact of surgical techniques and glucose require validation in larger studies. Liver Transpl 15:1852–1860, 2009. © 2009 AASLD.