OBJECTIVE To determine hemostasis variables in type I diabetic patients without clinically demonstrable micro- and macroangiopathy and to relate them to glycemic control. RESEARCH DESIGN AND METHODS Fifty patients and 50 comparable control subjects were enrolled in this study. The patients were subdivided in two groups, according to their level of HbA1c (group 1, n = 30, HbA1c ≤ 8% group 2, n = 20, HbA1c > 8%). We determined the platelet count, the platelet aggregation in the spontaneous state and in the presence of ADP or collagen, β-thromboglobulin, platelet factor 4, fibrinogen, von Willebrand factor (factors VIII:C, VIIIR:Ag, and VIIIR:VW), plasma and urinary fibrinopeptide A, euglobulin lysis time, anticoagulant proteins C and S, and plasma viscosity. RESULTS All coagulation variables were significantly higher in diabetic patients compared with control subjects. Moreover, when the patients were subdivided according to their levels of HbA1c, the hemostatic disturbances appeared significantly more pronounced in the poorly controlled than in the well-controlled subjects. CONCLUSIONS This study confirms the existence of a state of hypercoagulability in type I diabetes. This hypercoagulability may be related to poor glycemic control. Our study suggests that the hemostasis disturbances precede demonstrable vascular complications.