Objective: To correlate the APACHE-II score system with mortality and length of stay in ICU. Study Design: Cohort study. Place and Duration of Study: The Intensive Care Unit (ICU) of the Aga Khan University Hospital, Karachi, from May 2005 to May 2006. Methodology: All adult patients who were admitted in the ICU were included. APACHE-II score was calculated at the second and seventh days of admission in the ICU. Patients who were discharged alive from the ICU or died after first APACHE-II Score (at 2nd day) were noted as the primary outcome measurement. Second APACHE-II score (at 7th day) was used to predict the length of stay in the ICU. Pearson's correlation coefficient (r) was determined with significance at p < 0.05. Results: In the lowest score category 3-10, 27 out of 30 patients (90%) were discharged and only 3 (10%) died. Out of those 39 patients whose APACHE-II score was found in high category 31 - 40, 33 (84.6%) deaths were observed. This revealed that there might be more chances of death in case of high APACHE-II score (p=0.001). Insignificant but an inverse correlation (r = -0.084, p < 0.183) was observed between APACHE-II score and length of ICU stay. Conclusion: The APACHE-II scoring system was found useful for classifying patients according to their disease severity. There was an inverse relationship between the high score and the length of stay as well higher chances of mortality.