The aim of the present study is a literature revision of the contribution of continuous glucose monitoring system (CGMS) in the interpretation of HbA1c levels in type 1 diabetes (T1DM). We performed a revision of the efficacy, benefits, interpretation of methods and experience with this system. The CGMS could be useful in T1DM patients that present great glycemic variability or severe hypoglycemia (mainly nocturnal) and postprandial hyperglycemia. The identification of altered patterns or the glycemic variability allows therapeutic adjustment and improvement of the metabolic control. CGMS is a safe method with a rare occurrence of side effects and it is well-tolerated by patients. The extension of the procedure for more days, over the 72h period recommended by the standard test, allows us to get important data to changes and adjustments on the insulin management of the type 1 diabetes mellitus patients.