The Diabetes Control and Complications Trial (DCCT) provided much information towards settling the long-running controversy about the effectiveness of improving control of diabetes on the risk of its major complications. With the appearance or the advance of clinically significant retinopathy as its major outcome variable, DCCT randomised 1,441 insulin-dependent diabetic patients to conventional or intensified control groups. In both primary prevention and secondary intervention arms of the trial, intensified control reduced retinopathy risk by half or more, and also reduced nephropathy and neuropathy risks--however, risk of severe hypoglycaemic episodes was increased about three-fold. By contrast, there were no differences in quality of life, neurocognitive or emotional assessments between the two groups. The application of trial findings to 'real life' care is considered.