Acquired von Willebrand Syndrome (AVWS) is a rare coagulation disorder which can be associated with IgM-paraproteinaemia. Recently, recombinant von Willebrand factor (rVWF) has become available for the treatment of bleedings in patients with inherited von Willebrand disease, but experience in patients with AVWS is limited. We report on two patients with AVWS with underlying IgM paraproteinaemia with distinct underlying pathomechanisms. In one patient the paraprotein built unspecific complexes with von Willebrand factor. In the other patient, we were able to detect an IgM antibody against von Willebrand factor. Bleeding in this patient was successfully treated with rVWF. To our knowledge, this is the first report about the successful use of rVWF in a patient with AVWS with the detection of a von Willebrand factor-specific antibody.