Postprandial hyperglycemia is an independent risk factor for cardiovascular disease-related morbidity and mortality, not only in diabetes mellitus (DM) but also in impaired glucose tolerance. Postprandial glycemic levels have been difficult to monitor, but recently 1,5-anhydroglucitol (1,5-AG) levels have proven to be beneficial for this purpose. In humans, 1,5-AG, a 1-deoxy-glucopyranose, is a major and abundant polyol, of which 90% is derived from ingested food, and little is produced from glycogen in the liver. Nearly all 1,5-AG is reabsorbed in normoglycemia, but the reabsorption rate decreases in proportion to the degree of hyperglycemia above the renal threshold for glucosuria, which is 160 to 180 mg/dL. Glucosuria appears if the level of blood glucose rises above this level. The renal reabsorption of 1,5-AG is competitively inhibited by glucosuria. The 1,5-AG level appears to be well suited for monitoring glucose homeostasis in subjects with near-normoglycemia or with postprandial hyperglycemia without fasting hyperglycemia.