Urinary neutrophil gelatinase-associated lipocalin (uNGAL) has been identified as an early marker of acute kidney injury (AKI) in pediatric and adult populations. The aim of this review is to provide the most recent and relevant knowledge about the use of uNGAL as an early marker of renal failure and, possibly, of other morbid conditions in full-term and very low birth weight infants. A recently provided reference range for uNGAL in very low birth weight infants shows that normative values for this population are similar to those of older children and adults. Increased production of uNGAL is associated with AKI in young children undergoing cardiac bypass. uNGAL is acutely produced in critically ill newborns with or without AKI. Further studies to confirm uNGAL's potential to predict AKI in cardiac and noncardiac populations of newborns are required prior to utilizing this promising biomarker in clinical practice. The finding of markedly elevated uNGAL levels in critically ill newborns with normal renal function strongly suggests that uNGAL may have a role in the detection of nonrenal morbid conditions such as sepsis.