Diabetes mellitus and its complications are conditions of growing importance from both the clinical and epidemiological standpoint. Diabetes has life-threatening complications affecting several organs and systems, with increased risk for ocular, renal, cardiac, cerebral, nervous and peripheral vascular disease. In many developed countries and in special ethnic groups diabetes causes premature disability and mortality. It is, therefore, mandatory for both the specialist and the practitioner to be acquainted with the pathophysiological mechanisms, clinical manifestations and, above all, therapy of diabetes mellitus.