Objective : This study aims at (1) validating the use of Acute Physiology and Chronic Health Evaluation II (APACHE II) scoring system in the medical intensive care unit ( MICU) for prediction of the risk for mortality, (2) to compare the predicted death rate with the observed death rate of the patients gender wise and age wise. Design: Hospital based prospective study. Setting: Hospitals in South India, affiliated to medical colleges. Methods: A total of 350 patients admitted in the MICU between the age of 18-57 were enrolled for this study. APACHE II score was calculated in each patient on the day of admission within 24 hours. The predicted mortality was calculated on the basis of this score. Results: The mean APACHE II score was 9.42 ± 3.4. The ICU mortality rate within 24 hours after admission was 14%. The area under the Receiver operating characteristic curve (ROC curve) was 0.8 indicating good discrimination. The standardized mortality ratio (SMR) was 0.9. Conclusion: The study validates that APACHE II can be a reliable tool in predicting the mortality rate in MICU patients of Indian population within 24 hours of their admission.