Currently, we can make the following generalizations about the major long-term complications of diabetes. First, they occur commonly after 10 to 15 years of diabetes. Second, the complications of renal and retinal disease, but not of atherogenic and neurological disease, appear to be related to the severity of hyperglycemia. Third, some complications do not seem to be readily reversible by decreasing blood glucose for one to three years. Fourth, whether retinal and renal disease can be prevented or reduced by an early intervention is not yet known but is under intensive study. Fifth, the risks of some forms of intensive therapy include hypoglycemia, ketoacidosis, skin infection, weight gain, and poor adherence to arduous regimens. Finally, an analysis of the relationship of benefits to risk in intensive therapy is not yet possible and must await further study. Meanwhile, the diabetes research community will need to evaluate whether alternative procedures, e.g., aldose reductase inhibitors or islet transplants, might not be more reasonable than currently available modes of intensive therapy for reducing the long-term complications of diabetes.