It had been hoped for many years that intensive treatment of diabetes mellitus would reverse or defer significantly its major complications of microvascular and macrovascular disease, stroke, and heart attack, and be compatible with a healthy lifestyle.

While a general impression indicating that intensive and aggressive therapy was potentially a benefit, two major studies have recently provided much greater justification and clarification for control of diabetes mellitus. These two studies, the Diabetes Control Complications Trial research group and the United Kingdom Prospective Diabetes Study Group investigations, are reviewed in detail here to establish more clearly the rationale for close control of diabetes.