Introduction & Objective: Surgery in the elderly is an important part of surgery. In the last two decades, the number of surgeries in persons >65 years old has increased from 19% to 37% of all of surgeries. It is expected that the population of over 65 years old will increase from 12.7% to 20% by 2030. If we evaluate the risk factors and relationships between them and post operative morbidity and mortality, then we can decrease post operative complications by controlling the most common and the most important risk factors. Materials & Methods: From 1996 to 2006, 1000 patients with the age of >65 years old were operated (only laparatomy) under general anesthesia at Loghman Medical Center. The randomly selected patients were separated into three groups: 65 to 75, 75 to 85 and >85 years old. The duration of hospitalization and post operative complications and mortality of these patients were recorded and their relation with risk factors were evaluated. Results: This study included 624 men and 376 women. They were divided into three age groups among which 60.1% of the patients had no history of comorbidity and 39.9% had this history. Mortality in patients that had IHD was much more than those that did not have risk factors significantly. In three groups the mortality rate consisted of: 4.5% vs 1.5%, 6% vs 1% and 8.5% vs 2%. Duration of hospitalization in three groups were: 14 days vs 7, 20 days vs 11 and 28 days vs 18. Conclusions: In this study various kinds of comorbidity in patients were evaluated. Among these, IHD was the most common comorbidity that was associated with morbidity and mortality. This relationship was increased from >65 to >85 years old patients. On the other hand, we can decrease morbidity and mortality in the elderly through controls and aggressive treatment of cardiovascular system diseases and evaluations and controls of risk factors.