This randomized prospective study was carried on 40 critically ill children admitted to pediatric intensive care unit (PICU), Children’s hospital, Cairo University. There were 21 male and 19 female. Their ages ranged from 2 to 96 months. Two urine samples were taken from all patients; upon enrollment and 48 hours later, to assess level of urinary Interleukin-18 with monitoring of kidney functions by taking serum Creatinine samples at the same times. We found that urinary Interleukin-18 rises, prior to serum creatinine, in patients who developed acute kidney injury during their stay in the PICU and that could make urinary interleukin-18 an early acute kidney injury biomarker in critically ill children.