Hypophosphatemia is one of the common disorders that develop in critically ill patients .It has potential complications and is often unrecognized in those patients. Objective: Determining the incidence of hypophosphatemia in critically ill children, its association with clinical outcomes and the possible risk factors . Methods:50 patients were enrolled in the study. Levels of serum phosphate were measured on day 1 and day 7 of PICU (Pediatric intensive care unit) stay. The following variables were analyzed: age, gender, diagnosis on admission, malnutrition, phosphorus intake, clinical severity score on admission OFI (Organ Failure Index ) and daily scores PELOD (Pediatric Logistic Organ Dysfunction), sepsis, use of dopamine, furosemide and steroids and assessment of nutrition by z scores. Results: The incidence of hypophosphatemia on admission was 42%. On seventh day of admission incidence of hypophosphatemia was 62% . Malnutrition was present in 24% of patients, serum phosphorus level was significantly lower in malnourished than in well- nourished children (p value = 0.018), . Hypophosphatemia was associated with prolonged PICU length of stay (p