The fundamental role of good metabolic control has been demonstrated in type 1 and type 2 diabetes. Nevertheless, clinicians often wonder why some patients under good metabolic control develop complications while others remain free of such complications, despite a poorly controlled disease. The present study revisited material from the DCCT database, by classifying the 1441 patients as being under good or poor metabolic control if their HbA1c mean level fell in the lower (HbA1c<=6.9%) or upper (HbA1c>/=9.5%) quintile of the overall distribution of mean HbA1c levels observed in the DCCT population. The impact of metabolic control and of other potential factors related to the patient and his/her disease on the development and/or deterioration of complications, in particular diabetic retinopathy and nephropathy, was assessed. Although metabolic control is the major determinant of the risk of developing diabetic retinopathy and nephropathy, the study also emphasizes the significant role of other risk factors, in particularly BMI, disease duration, micro-albuminuria, HbA1c at baseline, gender and age on such complications. It is concluded that early control of the metabolic and clinical status of diabetic patients has major consequences on the evolution of the disease. Nomograms have been proposed to help the clinician in this task.