Chronic microvascular complications are important causes of mortality and morbidity in people with diabetes mellitus. After 10 years of disease, nearly 70% of diabetics are affected by retinopathy and about 40% by nephropathy. Genetic factors have a great influence on the development of diabetic microvascular complications, as pointed out by their association with HLA system and Na/Li countertransport, but epidemiological and experimental studies show that the greater role is played by the metabolic milieu. Protein glycation, sorbitol pathway and lipid abnormalities can be responsible for early and fast development of the microvascular complications of diabetes mellitus.