It is both common and wise practice to adjust the treatment of diabetic patients to obtain plasma glucose concentrations as close as possible to the "normal range", correcting both postprandial hyperglycaemic spikes and the less increased, but persistently high, plasma glucose concentration between meals. The Diabetes Control and Complications Trials (DCCT) and the United Kingdom Prospective Diabetes Study (UKPDS) have provided evidence that intensive treatment can prevent complications associated with diabetes mellitus. In both studies, effectiveness of hyperglycaemic treatment was assessed by means of the glycated haemoglobin level. This is an integrated measure of both postprandial and fasting hyperglycaemia. The absolute and relative importance of the two conditions, however, could differ depending upon the organ or system suffering from diabetic complications and other more or less known individual factors. This paper aims to emphasize the effects of acute hyperglycaemia, in particular, postprandial hyperglycaemia, on the development of diabetic complications. The role of oxidative stress as a mediator of acute hyperglycaemia is further discussed. More investigation in this area is required so that treatment can be eventually individualised. Perhaps, in some patients, efforts could be concentrated on the control of hyperglycaemic spikes and/or specific organ or system susceptibility to either acute or chronic hyperglycaemia.