Data on FVIII and VWF accumulation during prophylaxis in VWD are lacking.<h4>Objectives</h4>This study analyzed FVIII and VWF activity levels during long-term prophylaxis with wilate, a plasma-derived VWF/FVIII concentrate containing VWF and FVIII in a physiological 1:1 activity ratio, in the prospective WIL-31 study.<h4>Methods</h4>Preinjection and postinjection FVIII and VWF activity levels were measured in plasma at baseline and after 1, 2, 3, 6, 9, and 12 months of wilate in the 33 patients who completed WIL-31. Here, VWF is linked to von Willebrand disease (hereditary or acquired).