Non-insulin-dependent diabetes mellitus (NIDDM) affects approximately 12 million people in the United States. NIDDM is frequently found to coexist with other conditions, such as obesity, dyslipidemia, atherosclerotic vascular disease, and hypertension, which contribute to morbidity and mortality. Although the major clinical objective in the management of NIDDM is to control hyperglycemia, the long-term objective is to prevent microvascular and macrovascular complications. Cardiovascular disease is the major cause of death in NIDDM patients. Although hyperglycemia may be adequately controlled, risk factors for coronary heart disease may remain unchanged. Treatment with metformin controls hyperglycemia and may have positive effects on cardiovascular risk factors. When used alone or in combination with sulfonylureas, metformin tends to stabilize or decrease weight, maintains or reduces insulin levels, has beneficial effects on plasma lipid profiles, and may also have beneficial effects on blood pressure and the fibrinolytic system.