Biomarkers are biological parameters that can be objectively measured and evaluated, which act as indicators of normal or pathological processes, or of the response to intervention. Acute Kidney Injury (AKI) biomarkers must be easy to detect and measure, must correlate with severity (offering accurate prognosis), quantitatively describing the level of injury even in the absence of clinical signs. Finally, they must be adequate to indicate treatment initiation. So, the sensitivity (early appearance), specificity (typical of organ injury) and time-course are critical factors in determining the utility of a particular biomarker in the disease process. It is unlikely that a single biomarker will satisfy all of these requirements. As AKI is multifactorial in origin, a panel of biomarkers will be required on one hand to differentiate subtypes of AKI, on the other hand to define the phase and severity of injury. The aim of this review is to present the principal urinary biomarkers used in neonatology.