A case of acquired von Willebrand disease (AvWD) associated with an IgA lambda multiple myeloma is reported. No form of inhibitor could be detected. SDS-agarose gel electrophoresis patterns of von Willebrand factor (vWF) both in plasma and platelet lysates were normal but a decrease in all-sized multimers with a type IA pattern was seen. After 1-deamino-8-D arginine vasopressin (DDAVP) infusion, vWF multimers larger than those seen in the resting state appeared in patient plasma, which were progressively cleared. Indirect immunofluorescence studies with a monoclonal antibody to vWF showed that vWF was selectively absorbed into myelomatous cells. This is the first case of AvWD associated with multiple myeloma resulting from the selective absorption of vWF into abnormal plasma cells. This feature established a new pathophysiological mechanism of AvWD in multiple myeloma and probably in other lymphoproliferative diseases.