Background: Hypophosphatemia is a metabolic disorder that can have significant consequences and is frequently undiagnosed in critically ill children. While hypophosphatemia is typically characterized by nonspecific symptoms such as weariness and irritation, severe hypophosphatemia (less than 1.0 mg/dl) can result in much more severe complications including such decreased diaphragmatic contractility and cardiac arrhythmias. Aim of the Study: Determine the prevalence of hypophosphatemia in critically ill children, as well as the clinical consequences and risk factors associated with the condition throughout patients' admission in the PICU. Patients and Methods: A case-control study that was conducted over a period of one year, from July 2019 to June 2021, at PICU of Pediatrics Department, Zagazig University Hospitals.The study included 180 subjects that were classified into two groups, each of 90 subjects as follows; patients group, which included 90 cases, and the control group, which included 90 healthy infants and children. Results: There was a statistically significant difference in weight, height percentile, ESR and CRP, hemoglobin level, TLC, PT, INR, alkaline phosphatase a serum, serum creatinine, PH, serum phosphorus level, presence of hypophosphatemia (20%), number of patients with hypophosphatemia, percent change in serum phosphorus, as well as percent change in serum phosphorus between the studied groups. Conclusion: In our investigation, the obvious probable source of hypophosphatemia was prolonged TPN decision-making as well as sepsis. In the PICU, mild to moderate hypophosphatemia occurred. Hypophosphatemia was related with an increased length of stay in the PICU and poor outcomes.