Large randomised studies have established that early intensive glycaemic control reduces the risk of diabetic complications, both microvascular and macrovascular. However, epidemiological and prospective data support a long-term influence of early metabolic control on clinical outcomes. This phenomenon has recently been defined as 'metabolic memory'. Furthermore, evidence suggests that 'glucose variability' may also be an independent risk factor for cardiovascular complications in diabetes. Studies suggest that all these different situations of hyperglycaemia share a common pathogenetic mechanism, increased oxidative stress, producing an endothelial dysfunction. The therapeutic challenge derived from these evidences is a need not only for an early tight glycaemic control, but also for maintaining glycaemia within a strict normal narrow range.