The most serious complication of diabetes mellitus is clinical nephropathy. The development of persistent proteinuria (urinary excretion of more than 300 mg albumin/24 hours) implies an extremely high risk of early death. Renal failure is the most frequent cause of death but the mortality of cardiovascular diseases is also increased. Besides the link between albuminuria (nephropathy) and atherosclerosis in coronary arteries, albuminuria is also a predictor of microangiopathy in other organs than the kidneys. The annual incidence of proliferative retinopathy in early nephropathy is 10-15% compared to only 1% in patients without nephropathy. Also signs of cardiomyopathy have been demonstrated in early nephropathy. Further we have described markers of universal endothelial damage in these patients, and we hypothesize that albuminuria not only is a predictor of renal disease but also of widespread vascular disease. Long-term improvement of metabolic control by use of insulin infusion pumps and early antihypertensive treatment seem to stop the further progression of early diabetic nephropathy and to significantly improve the prognosis of clinical nephropathy.