Background: Little is known of the exact causes of death and the impact ofgeneral risk factors that may complicate the course of critically ill patients.Scoring systems for use in ICU patients allow an assessment.Objectives: Apply commonly used scores for assessment of illness severityand determine their relation to patient outcome. And identify thecombination of factors capable of predicting patient’s outcome.Methods: This study included 231 patients were admitted to PICU of CairoUniversity Pediatric Hospital over one year. PRISM III, PIM2, PEMOD,PELOD, TISS and SOFA scores were obtained for every patient within theday of admission and patients were evaluated on follow up using SOFAscore and TISS. Then each score parameter was evaluated separately.Results: Significant positive correlations were found between PRISM III,PIM2, PELOD, PEMOD, SOFA and TISS on the day of admission andmortalities of PICU (p<0.0001). TISS and SOFA score had the highestdiscrimination ability (area under ROC curve: 0.81, 0.765 respectively).Also significant positive correlations were found between SOFA score andTISS scores on day 1, 3 and 7 and mortalities of PICU (p<0.0001). TISS hadmore ability of discrimination than SOFA score on day 1 (area under ROCcurve 0.843, 0.787 respectively). Other factors that increase risk of mortalitywere longer length of stay, mechanical ventilation, vaso-active drugs anddialysis.Conclusion: Scoring systems applied in our PICU had good discriminationability. TISS was a good tool for following up patients. LOS, use ofmechanical ventilation and inotropes were risk factors of mortality.