To answer these questions a questionnaire is developed, which will be sent to the study population. In addition, blood will be drawn for von Willebrand factor measurement and plasma and DNA will be stored. The relationship between laboratory parameters, (including von Willebrand factor, FVIII and prothrombotic coagulation disorders) and the clinical phenotype in patients with moderate and severe von Willebrand disease will be studied. We will assess the effect of the laboratory parameters on both the severity of bleeding tendency, and the possible protecting effect on the risk of arterial thrombosis. In the future mutation analysis of the VWF gene will be performed in patients with moderate and severe von Willebrand disease in the Netherlands.