Summary A case of acquired von Willebrand's disease (AvWD) associated with an adrenal cortical carcinoma is reported. The circulating highest molecular weight multimers (HMWM) of von Willebrand factor (vWF) were decreased when assessed by SDS-agarose plasma electrophoresis, leading to the diagnosis of type II AvWD. No forms of inhibitor could be detected in the plasma of the patient. In contrast, indirect immunoperoxidase studies with a monoclonal antibody to vWF demonstrated an absorption of vWF into malignant cells. Infusion of a vWF-FVIII concentrate, containing significant amounts of HMWM of vWF, allowed surgical resection of the tumour. After the first infusion of the concentrate, the vWF-RCo recovery was found to be low (38%) compared to the vWF:Ag (75%) and FVIII:C (163%) recoveries. The resolution of all biological signs of vWD, including the abnormal multimeric pattern, in the postoperative period was prompt and permanent. Therefore, the absorption of the HMWM of vWF by carcinomatous cells appears to represent a likely pathophysiological mechanism responsible for the AvWD syndrome in this patient.