Diabetes mellitus is associated with a variety of vascular complications like diabetic retinopathy, myocardial infarction, stroke and peripheral vessel disease. These complications are of utmost importance because they lead to disability and premature death of the patients. The pathogenesis of these lesions has been thought to depend at least partly on defects in the hemostatic system. Many alterations of the coagulation and the fibrinolytic system as well as of the reaction of platelets have been found in diabetics. In general these tend to suggest a state of slightly activated coagulation, of increased platelet reactivity and of decreased fibrinolysis. However, no conclusive picture of the role of hemostasis in the development of vascular lesions in diabetics has emerged yet, as contradictive results have been found by many investigators. The aim of this review article is to sum up the knowledge that has accumulated in the last years in controlled clinical trials concerning the state of the diabetic hemostatic system.