Background: The Red blood Cell Distribution Width (RDW or RCDW) is a measure of the variation of the Red Blood Cell (RBC) volume that was reported as part of the standard complete blood count. In the past, RDW was used for the differential diagnosis of anemia. RDW had been demonstrated to be significantly ssociated and changed with mortality and other different outcomes in various clinical conditions. Our study aimed to studying the prognostic effect of red cell distribution width and its clinical implications on critically ill children admitted to the Pediatric Intensive Care Unit (PICU). Methods: This was a prospective cohort study of critically ill children admitted to Pediatric Intensive Care Unit (ICU), Zagazig University Hospitals during the period of 6 months Including 40 critically ill children, their age from 1 month to 14 years. We limited our analysis to include patients under 14 years and in whom CBC including RDW was obtained at 1st day,4th day and 7th day of PICU admission. Results: This study showed that statistically significant difference between the studied patients regarding RDW on 1st, 4th, 7th days and RDW with different heamatological indices and different outcomes. Conclusion: RDW is a significant prognostic factor for hospital mortality in critically ill patients.