The United Kingdom Prospective Diabetes Study, the most ambitious single study of the treatment and nature of type 2 diabetes to date has two and nature of type 2 diabetes to date has two aspects: (i) as a clinical trial it has established that intensified glucose and blood pressure control significantly reduce the micro- and macrovascular complications of type 2 diabetes; (ii) in addition, because of its size and duration and the density of the data collected, it provides unparalleled information on the nature and natural history of the disease. It has defined the major importance of hyperglycaemia and hypertension as risk factors for complications and with the trial results provides the rationale and the goals for therapy. However, identification of the progressive deterioration of beta-cell function and the relative inefficacy of currently available therapies has posed major challenges to the achievement of these goals. Like all classic studies it raises more questions for further investigation.