The prevalence of diabetes in hospitalized adults is conservatively estimated at 12-25% and rising. Poor glucose control and presence of diabetes complications (e.g. diabetic nephropathy, diabetic neuropathy, atherosclerosis) are commonly regarded as risk factors for perioperative morbidity and mortality. Thus it is crucial to determine diabetes comorbidities preoperatively in order to avoid perioperative renal and cardiovascular complications. Perioperative glycemic control is challenging due to preoperative changes in diabetes treatment and the effects of surgery-associated stress hyperglycemia. For patients in general surgical units, evidence for specific glycemic goals is based on epidemiologic and physiologic data rather than clinical trials. According to guidelines of the German Society of Nutrition, the approximation of normoglycemia is reasonable as long as hypoglycemia is avoided (suggested range for plasma glucose 80-145 mg/dL).