There is a growing body of evidence that the sole use of hemoglobin A1c is insufficient to adequately reflect the metabolic situation of patients with diabetes mellitus. The risk of developing diabetes-related complications apparently not only depends on the long-term stability of glucose values, but also on the presence or occurrence of short-term glycemic peaks and nadirs lasting for minutes or hours during a day. This leads to the phenomenon of glycemic variability. This article reviews the existing evidence for the clinical relevance of short-term glucose variations and the currently available different means of measuring glycemic variability.