Diabetes mellitus is an independent risk factor for coronary artery disease. However, recently, it has been demonstrated that, irrespective of the presence of diabetes mellitus, altered glycemic levels are associated with adverse outcomes in patients suffering from stable coronary artery disease. Moreover, both hyperglycemia and hypoglycemia, either at the time of hospital admission or during coronary intervention, are linked to worse long and short-term prognosis in acute coronary syndromes. Thus, many efforts aiming at the monitoring of the glycemic status and prevention of excessive glycemic fluctuations have been made and striking evidences on the need for a stricter glucose homeostasis control have been collected. The purpose of this review is to summarize the most current and significant knowledge on the monitoring of glycemic status, its clinical impact on the prognosis of patients with coronary artery disease and its in-hospital management.