Background: Diarrhea-associated hemolytic uremic syndrome (D+HUS) causes acute renal failure. Neutrophil gelatinase-associated lipocalcin (NGAL) is an early indicator of kidney injury. Objective: To determine if urinary NGAL excretion is a biomarker of severe renal injury and predicts the need for dialysis in D+HUS. Methods: Patients were randomly selected from among participants in the SYNSORB Pk trial. Urine samples were collected daily if available during the first week of hospitalization. NGAL levels were determined by ELISA. Results: 34 children, age 5.9±3.9 yr, were studied; ten (29%) required dialysis. Patients were categorized based on urinary NGAL concentration within five days of hospitalization - <200 ng/ml and ≥200 ng/ml. Twenty patients (58%) had increased urinary NGAL excretion. The severity of D+HUS at enrollment was similar in the two groups. However, children with increased urinary NGAL levels had higher peak BUN and creatinine concentrations (P<0.01) and required dialysis more often, 9/20 versus 1/14 (P=0.024) compared to children with normal excretion. Conclusion: The majority of patients with D+HUS have renal tubular epithelial injury, as evidenced by elevated urinary NGAL excretion. Urinary NGAL levels below 200 ng/ml within five days of hospitalization may be an adjunctive marker that defines less severe renal involvement.