We studied thirty diabetic patients and we evaluated their knowledge of main topics of diabetes mellitus. The level of the knowledge was evaluated by multiple choice questionnaires. On the basis of score obtained the patients were divided into two groups: Group A, with high knowledge level, Group B, with low knowledge level. All the patients were followed-up for a 12 months period after a careful education. At the end of follow-up, we compared the Group A patients with another group of 14 diabetic children, who have followed an educational programme from the diagnosis of the disease (Group C). We assessed the knowledge score and the principal metabolic parameters in the three groups of patients; during the follow-up, we found a significant increase of these parameters in Group A and B patients, more evident in Group A patients. At the end of follow-up, the Group C patients showed a higher knowledge score and metabolic parameters than the Group A children. This study shows that education of disease is important for the increase of metabolic parameters and its usefulness is higher if is carried out from the onset of the disease.