Microvascular complications of diabetes include retinopathy, nephropathy and neuropathy. The first signs of these complications may develop in children and adolescents, particularly if insulin treatment has been inadequate. The mechanisms by which diabetic microangiopathy develop are not known, but probably include genetic influences. Several biochemical changes may interact, one important change being increased protein glycation. Important functional changes are increased organ blood flow, increased vascular permeability, abnormal blood viscosity and abnormal platelet and endothelial function. The structural hallmark of diabetic microangiopathy is the thickening of the capillary basement membrane. These changes may lead to occlusive angiopathy and to tissue hypoxia and damage. Screening for microangiopathy should start in children and adolescents after 5-y duration of the disease and 10y of age. The screening should include retinal examination through a dilated pupil or fundus photography, urinary albumin excretion rate, blood pressure measurement and neurological examination. Several intervention trials have shown that near normoglycaemia may reduce the risk of microangiopathy. There is a curvilinear association between the risk of development and progression of microangiopathy and mean blood glucose. Therefore, optimal insulin treatment is important in children and adolescents.