We describe a man and his daughter from a large New Zealand family with the extremely rare variant von Willebrand's (VW) disease type IID. These two patients had a severe bleeding history following minor surgery and displayed easy bruising. However, routine laboratory screening tests and factor VIII studies were essentially normal except for slightly reduced ristocetin cofactor activity and prolonged skin bleeding times. Although lacking higher molecular weight forms of VW antigen in common with VW type II's the patients' multimer patterns were clearly different from types IIA and IIB. Instead of showing the characteristic 'triplet' pattern in each multimer band the patients gave a single prominent band with faint satellite bands different in mobility to those in normals. Von Willebrand factor from the patients' platelets gave a similar abnormal pattern. DDAVP failed to correct the bleeding time in either patient and multimer analysis confirmed that there was no increase in the higher molecular weight VWF antigen.