Diabetes mellitus is likely to become one of the most prevalent and economically important diseases of the 21st century largely owing to an increasing incidence of type 2 diabetes mellitus (DM) in the developed nations and many of the developing nations. Every physician will encounter a patient who has diabetes. Multiple factors, both environmental and genetic, contribute to the pathogenesis of the disease. Type 2 DM is particularly common in obese sedentary populations, while type 1 DM can have a dramatic onset and be a major therapeutic challenge.