The American Diabetes Association (ADA) has recently revised the system of classification and criteria for diagnosis of diabetes to help remedy the problem of undiagnosed diabetes, as well as to move away from a system of diagnosis based on treatment used toward a system based on disease etiology. The ADA report identifies 4 major categories of diabetes: (1) type 1 (absolute insulin deficiency); (2) type 2 (insulin resistance with an insulin secretory defect); (3) other specific types; and (4) gestational diabetes mellitus. The major changes are establishing a fasting glucose > or = 126 mg/dL for the diagnosis of diabetes and the suggestion that oral glucose tolerance tests are not needed in routine practice for the diagnosis of diabetes. The report stresses that the degree and type of diabetes can change over time and underscores the importance of early recognition and management of glycemic disorders. More aggressive screening, using fasting plasma glucose (FPG) concentrations of > or = 110 mg/dL as a marker of insulin resistance, should help identify not only patients with hyperglycemia but also those with insulin resistance without significant hyperglycemia. Even if hemoglobin A1c levels are in the normal range, patients in this category are at increased risk for developing macrovascular complications and may benefit from active intervention to reduce cardiac risk factors.