Diabetes mellitus is a large social and clinical problem. Its detection at the earliest stages and regular monitoring is very important especially in type 2 diabetes, which has a long asymptomatic phase, but during which diabetes late complications are developing. The plasma glucose levels should be brought closely to a normal range as soon as possible because it allows to prevent and slow down the progression of micro– and macrovascular complications. On the one side this beneficial effects persist also after patients return to usual glycaemic control. On the second side despite good current compensation of glycaemia the vascular complications are developed. This phenomenon is called as ‘metabolic memory’. As the main causes of this effect is the proteins glycation, especially mitochondrial proteins, and excessive generation of reactive oxygen species are indicated. Apart this the other paths of glucose transformations (such as polyol, hexosamine and proteins kinase C pathways) are intensified and also escalates an oxidative stress. The appropriate and rigorous early hypoglycaemic therapy is very important to prevent complications. In type 2 diabetic patients introducing treatment of insulin, according to principle ‘switch on – switch off’ just from the beginning of disease has been proposed. Applying antioxidative medicines is also suggested. The management of the ‘metabolic memory’ could be an important strategy for the prevention and reduce of vascular late complications in both types of diabetes.