Olive oil, the main fatty component of the Mediterranean diet, is characterized by consisting of monounsaturated fatty acids as well as by its elevated content in antioxidant agents. This oil exhibits numerous biological functions which are beneficial for the state of health. A diet rich in monounsaturated fatty acids provides an adequate fluidity to the biological membranes, diminishing the hazard of lipid peroxidation which affects polyunsaturated fatty acids. Moreover, the antioxidants present in olive oil are able to scavenge free radicals and afford an adequate protection against peroxidation. Regarding the heart, olive oil decreases the plasmatic levels of LDL-cholesterol and increases those of HDL-cholesterol, hence diminishing the risk of suffering from heart complaints. In this context, it has been suggested that increased consumption of monounsaturated fatty acids in place of polyunsaturated fatty acids will render circulating lipoproteins less sensitive to peroxidation and thereby diminish the development of atherosclerosis. Olive oil has also been proven to contribute to a better control of the hypertriglyceridemia accompanying diabetes and may reduce the risk of breast cancer and colorectum. On the other hand, several investigations have suggested that olive oil can be beneficial in inflammatory and autoimmune diseases, such as rheumatoid arthritis. In this sense, some reports have indicated that olive oil modifies inflammatory cytokines production. As for the digestive system, olive oil enhances gallbladder emptying consequently reducing cholelithiasis risk, decreases the pancreatic exocrine secretion and gastric secretory function in response to food. Finally, it has been demonstrated that a diet rich in olive oil is associated with a high percentage of gastric ulcer healing and affords a higher resistance against non steroidal antiinflammatory drugs-induced gastric ulcerogenesis.