The Diabetes Control and Complications Trial, which ended in 1993 after a mean of 6.5 years, demonstrated that intensive diabetes therapy with the goal of achieving glycemia as close to the normal range as possible decreased the occurrence of diabetes specific complications (retinopathy, nephropathy, and neuropathy) by as much as 75 percent when compared with conventional therapy that did not have a specific glycemic target. The benefit of intensive therapy was demonstrated in relatively healthy Type 1 diabetic patients with either no complications at baseline or with minimal to moderate complications at baseline. The DCCT also demonstrated the relative risks of such intensive therapy, including a three-fold increase in severe hypoglycemia and weight gain. The balance between benefit and risk was judged to favor intensive therapy as the recommended treatment for most patients with Type 1 diabetes. A large number of unanswered questions remain in the wake of the DCCT. First, the history and risk factors for cardiovascular disease in the setting of Type 1 diabetes, which is the major cause of mortality in the Type 1 diabetic population, remains poorly understood. Second, although the DCCT demonstrated a uniform and substantial effect of intensive therapy on long-term complications, whether the benefit of intensive therapy demonstrated will carry over and be translated into a decrease in the more advanced stages of complications is largely unknown. In particular, any long-term benefit of intensive therapy on the ultimate development of end-stage renal disease requires further examination. Third, the ability of volunteers previously treated in the DCCT to maintain long-term diabetes control, and the medical care provided to them in the non-study setting is of great interest.