Type 2 diabetes mellitus is a heterogeneous disorder characterized by 2 pathogenic defects, impaired insulin secretion and insulin resistance. The resultant hyperglycemia causes microvascular and macrovascular complications that increase morbidity and mortality in patients with diabetes mellitus. Optimum glycemic control in patients with type 1 and type 2 diabetes mellitus prevents the development of microvascular disease and, to a lesser extent, macrovascular disease. Prandial hyperglycemia may be an independent risk factor for the development of diabetic complications. This article reviews the pathophysiologic mechanisms of glucose metabolism and describes the results of epidemiological and interventional studies that have demonstrated the association of acute and chronic hyperglycemia with the development of diabetic complications. The American Diabetes Association has defined diagnostic and treatment goals for diabetes mellitus, striving to achieve near-normal glycemic control to delay or prevent the development of diabetic complications. A number of oral antidiabetic agents and insulins are currently available for the treatment of type 2 diabetes mellitus in the United States. These agents target fasting and postmeal plasma glucose levels to improve glycemic control. Alone or in combination, these agents have enhanced the clinical approaches to treating diabetes mellitus.