Background: ICU scoring systems allowed an assessment of the severity of disease and death prediction. The use of prognostic scoring system to predict possibility of mortality and evaluating outcomes in critically ill patients is an important in the modern evidence –based critical care. Aim: This study aimed to assess prognostic scoring systems as a tool to predict the clinical outcomes for patient with critical condition. Design: A descriptive exploratory design was conducted to achieve the aim of this study. Setting: The study was carried out in intensive care units (ICUs) of Ain Shams University Hospital (surgical, Internal medicine and neurological ICUs) affiliated to Ain Shams University, Cairo-Egypt. Study subject: A Purposive sample of (200) patients admitted to the previous mentioned setting. Tools of data collection; were consisted of patient assessment tool, APACHE IV, SAPS III, SOFA and MPM II and the last tool was used (at admission MPM0, MPM at 24hrs, MPM at 48hrs and MPM at 72 hrs). Results: Revealed that, more than half of studied patients were male, with age ranged from 23.00 to 80.00 years old. The overall mortality observed was 25% in all the patients. APACHE IV predicted mortality rate sensitivity and specificity were 94.11% and 95.97% respectively. Also, APACHE IV score had moderate positive correlation between predicated ICU length of stay and real ICU length of stay. Conclusion: APACHE IV established the best discrimination and superior calibration makes it the most appropriate model for comparisons of mortality rates with the other scores in ICU. APACHE IV score was better than SAPS III, SOFA and MPM II scores as they were significantly higher between non-survivors to predict mortality and length of stay among ICUs patients. Recommendations: Applications of APACHE IV score system to assess of all admitted patient to ICU in nursing assessment