Background: Elderly patients are a significant and increasing proportion of ICU patients. With advancing age, the comorbidities critically ill elderly patients have substantial mortality. The early recognition of patients at high risk of mortality is needed to plan care in advance and to control healthcare costs. Aim: To find out the relation between chronic diseases and outcome in critically ill elderlyadmitted to ICU. Study design: A prospective study. Participants: seventy elderly patients aged 60 years and above. Method: This study was performed in Geriatric ICU in Ain Shams University Hospitals including 70 critically ill elderly patients admitted for 24 hours or more. Each patient was subjected to on admission clinical assessment including detailed history taking, in addition to laboratory investigations. Results: The results of our study showed that ischemic heart disease was the only chronic diseases that had significant statistical effect on mortality in critically ill elderly admitted to ICU with p. value= 0.002. Conclusion: In the current study we found that mortality was associated with history of ischemic heart disease.