The Glycemic Index (GI) is a rating system that ranks carbohydrate-containing foods according to their postprandial blood glucose response relative to the same quantity of available carbohydrate of a standard such as white bread or glucose. The concept of GI was first introduced in the early 80's by Jenkins and coworkers. Since then, numerous trials have been undertaken, many indicating benefits of a low GI diet on glycemic control, as well as lipid profiles, insulin and C-peptide levels, inflammatory and thrombolytic factors, endothelial function and regulation of body weight. As a result, a low-GI diet may prevent or delay the vascular complications of diabetes. However, despite many studies supporting the benefits of the Glycemic Index as part of the treatment of diabetes mellitus, several areas of controversy have been raised in the literature and are addressed here. Clinicians treating diabetic patients should be aware of the potential benefits of low-GI foods in the prevention and treatment of diabetes and its complications.