The monitoring of glycemia is an essential component of diabetes care. It may be divided into self-monitoring of blood glucose (SMBG), which measures the immediate level of glycemia, and measurement of hemoglobin A1c (HbA1c), which reflects longer-term glycemia. SMBG was discussed in an earlier review. HbA1c is a measure of erythrocyte hemoglobin glycation, and since erythrocytes have about a 120 day life span, HbA1c reflects mean glycemia for the previous 3 months (weighted to the most recent month). There are several conditions that confound the HbA1c measurement such as hemolytic anaemia (lowers HbA1c) or aplastic anaemia (raises it), but in most circumstances HbA1c is a valid index of glycemia. The recommendation is to measure HbA1c every 3-6 months, and treat to a target level of < 7%. If these recommendations were successfully followed in most people with diabetes, long-term complications, especially microvascular complications, would be markedly reduced.