An estimated 246 million people worldwide have diabetes. Diabetes is a leading cause of death in most developed countries, and is reaching epidemic proportions in many developing and newly industrialized nations. Poorly controlled diabetes is associated with the development of renal failure, vision loss, macrovascular diseases and amputations. Large controlled clinical trials have demonstrated that intensive treatment of diabetes can significantly decrease the development and/or progression of microvascular complications of diabetes. There appears to be no glycaemic threshold for reduction of diabetes complications; the lower the glycated haemoglobin (HbA1c), the lower the risk. The progressive relationship between plasma glucose levels and cardiovascular risk extends well below the diabetic threshold. Until recently, the predominant focus of therapy has been on lowering HbA1c levels, with a strong emphasis on fasting plasma glucose. Although control of fasting hyperglycaemia is necessary, it is usually insufficient to obtain optimal glycaemic control. A growing body of evidence suggests that reducing postmeal plasma glucose excursions is as important, or perhaps more important for achieving HbA1c goals. This guideline reviews the evidence on the harmful effects of elevated postmeal glucose and makes recommendations on its treatment, assessment and targets.