Diabetes mellitus is a common disease that interferes with the body's ability to store energy from food. The pancreas makes a substance called insulin that helps to store energy from food. Type 1 diabetes mellitus (also called juvenile diabetes) occurs when the pancreas stops making insulin. In type 2 diabetes mellitus (also called adult-onset diabetes), the body makes plenty of insulin but is unable to use it normally. In both cases, the result is high blood sugar levels. Over time, high blood sugar levels can lead to blindness, kidney failure, nerve damage, and heart disease. Fortunately, good care with diet, exercise, and medications to keep blood sugar under control can prevent the development of these serious, costly complications. The control of blood pressure and cholesterol is also very important for patients with diabetes. Because it is possible to accomplish so much with good care, it is important to know about the general quality of diabetes care in the United States. To date, no one has provided a “national report card” to show how well the United States is achieving the promise of medical care for diabetes.