Acquired von Willebrand syndrome (AVWS) is a rare bleeding disorder with laboratory findings similar to those for congenital von Willebrand disease (VWD). Unlike VWD, AVWS usually occurs in individuals with no personal or family history of bleeding. The prevalence of AVWS in the general population is unknown because data from large prospective studies of this syndrome are not available. Although AVWS is more frequently associated with lympho-myeloproliferative and cardiovascular disorders, it can also occur in solid tumors and in immunological and other miscellaneous conditions. Among these miscellaneous conditions, hypothyroidism has been associated with AVWS type 1 with a frequency of ~2 to 5%. In the 47 cases reported in the literature, the low VWF is apparently due to a reduction in its synthesis and/or secretion. Diagnosis of AVWS is based on assays measuring the level and activity of von Willebrand factor (VWF). These tend to be low, whereas factor VIII (FVIII) coagulant activity can be normal. In patients with AVWS associated with hypothyroidism, mucocutaneous bleeding episodes are the most frequent and can be managed with local therapy and/or systemic administrations of antifibrinolytic agents and desmopressin. VWF/FVIII concentrates have been used in only a few patients. The use of thyroid hormones can reverse this abnormality.