von Willebrand factor in head and neck cancer. Laboratory abnormalities in blood coagulation factors are common in patients with cancer but the significance is unknown. Twenty-eight patients with head and neck cancer were studied at the time of diagnosis. Twenty-five were advanced-stage (III or IV) patients. Levels of clotting factors, antithrombin III, and plasminogen were normal. Levels of von Willebrand factor (vWF), both antigenic and functional (ristocetin cofactor), were elevated. This group of patients were followed for a minimum of 41 months (median, 48 months). Fifteen patients died within the follow-up period. von Willebrand factor levels were significantly higher in these 15 than the 13 survivors. Extreme elevation of ristocetin cofactor (greater than 300 U/dl) was seen in six of the 15 patients who died and in none of the survivors. Plasma vWF is elevated in head and neck cancer and the level measured at the time of diagnosis may have prognostic and potentially therapeutic implications. 