The concept of glycaemic index (GI) was developed 25 years ago by Jenkins and co-workers in 1981 and first studied to help diabetic patients with blood glucose control. In 1997 two epidemiological studies were published showing that high GI food consumption is associated with an increased risk of type 2 diabetes. At the same time the concept of the glycaemic load (GL) was introduced, based on GI and total carbohydrate intake. Since then, many studies have been conducted to investigate the role of dietary GI and GL in the prevention and management of type 2 diabetes, cardiovascular disease, obesity and other chronic diseases such as cancer. The current review will focus on the epidemiological evidence obtained so far. In addition, several key methodological issues will be addressed, such as the dietary assessment method used, the application of the international GI and GL table, and the correlated dietary patterns.International Journal of Obesity (2006) 30, S66-S71. doi:10.1038/sj.ijo.0803495.