| 6 | Hematology Meeting Reports 2007;1(3):6-19

von Willebrand disease (VWD) is the most frequent inherited disor-der of hemostasis and is due to quantitative (VWD type 1 and 3) or qualitative (VWD type 2) defects of von Willebrand factor (VWF). Due to the large heterogeneity of VWF defects and to the external variables (blood groups and other physiologic modifiers) influencing VWF levels in the circulation, VWD diagnosis can be difficult espe-cially in relatively mild forms. Three criteria should be always satis-fied for a correct VWD diagnosis: 1) a positive bleeding history in the patients; 2) reduced levels of VWF activity in plasma; 3) a positive family history suggestive of VWD. According to the most recent clin-ical prospective studies, bleeding history in the patients and in their family members should be now derived from a detailed question-naire on 11 bleeding symptoms and a bleeding severity score (BSS) can be calculated. The ristocetin cofactor activity of VWF (VWF:RCo) is the most useful test for VWD screening in the general populatio