Introduction: The APACHE II scoring system has been promulgated as a useful tool in the assessment of the severity of disease and prognosis for patients with acute-on-chronic medical conditions. The purpose of this study was to assess the statistical association of APACHE II score and multiple variables in ICU patients. METHODS Prospective data on 803 ICU patients for validation of the APACHE II system were analysed. We evaluated the relationship between APACHE II scores within the first 24 hours of ICU admission and multiple variables that included days in the ICU, mortality rate and age. The patients were classified as operation and nonoperation, survival and nonsurvival groups. RESULT 1) The APACHE II score was significantly higher in the 153 nonsurvivals (23.97+/-10.98) than in the 651 survivals (11.51+/-6.14) (p<0.05). 2) The mean APACHE II score of the nonoperation group (14.52+/-9.29) was significantly higher than operation group (12.40+/-7.30) (p<0.05). 3) The overall mortality rate was 17.8%. 4) All patients with an APACHE II score over 40 died. CONCLUSION The APACHE II score is statistically related with the mortality of critically ill patients.