Acquired von Willebrand's syndrome. Therapeutic and diagnostic implications. Acquired von Willebrand's syndrome is a newly recognized bleeding diathesis thought to be caused by autoantibodies to the von Willebrand factor. Acquired von Willebrand's syndrome has been reported in association with lymphoproliferative disorders and benign monoclonal gammopathies. Clinical features and laboratory abnormalities of this disease are similar to congenital von Willebrand's disease, but the optimal treatment may differ. We describe a 75-year-old man with chronic lymphocytic leukemia and recurrent epistaxis and also discuss the pathogenesis, diagnosis, and treatment of both the congenital and acquired disorders. 