Background: Little is known about the exact causes of death and the impact of general risk factors that may complicate the course of critically ill patients, different scoring systems used for assessment illness severity and outcome in ICU patients. Objectives: Application of commonly used scores for assessment of illness severity and determine their relation to patient outcome. And identify the combination of factors capable of predicting patient's outcome. Patients and Methods: This study included 100 patients who enrolled in a prospective observational cohort study. All were admit to pediatric ICU in Bab El-Sha'reya University Hospital over a period of 8 months duration (from January to August 2016). Pediatric Risk of Mortality (PRISM) III, Pediatric Multiple Organ Dysfunction (PEMOD) scoring system, Pediatric Logistic Organ, Dysfunction(PELOD) scoring system, Pediatric Index of Mortality 2 (PIM2), Sepsis-related Organ Failure Assessment (SOFA) scorewere obtained for every patient within the day of admission and patients were evaluated on follow up using SOFA score.  Each score parameter was evaluated separately. Results: Significant positive correlations were found between PRISM III, PIM2, PELOD, PEMOD and SOFA on the day of admission and mortalities of PICU. SOFA score had the highest discrimination ability (area under ROC curve: 0.765). Significant positive correlations were found between SOFA on day 1, 3 and 7 and mortalities of PICU. Other factors that increased risk of mortality were longer length of stay, mechanical ventilation and dialysis. Conclusion: Scoring systems applied in our PICU had good discrimination ability. PIM2 score discriminated well between survival and non-survival at our PICU. PELOD score can measure the severity of organs dysfunction and significantly correlated to mortalities in our PICU. SOFA score was a good tool for following up patients. Length of stay, use of mechanical ventilation and dialysis were risk factors of mortality. Patients admitted with MODS had highest mortality rates.