New recommendations for the classification and diagnosis of diabetes mellitus include the preferred use of the terms "type 1" and "type 2" instead of "IDDM" and "NIDDM" to designate the two major types of diabetes mellitus; simplification of the diagnostic criteria for diabetes mellitus to two abnormal fasting plasma determinations; and a lower cutoff for fasting plasma glucose (126 mg per dL [7 mmol per L] or higher) to confirm the diagnosis of diabetes mellitus. These changes provide an easier and more reliable means of diagnosing persons at risk of complications from hyperglycemia. Currently, only one half of the people who have diabetes mellitus have been diagnosed. Screening for diabetes mellitus should begin at 45 years of age and should be repeated every three years in persons without risk factors, and should begin earlier and be repeated more often in those with risk factors. Risk factors include obesity, first-degree relatives with diabetes mellitus, hypertension, hypertriglyceridemia or previous evidence of impaired glucose homeostasis. Earlier detection of diabetes mellitus may lead to tighter control of blood glucose levels and a reduction in the severity of complications associated with this disease.