Von Willebrand disease (VWD) is a bleeding disorder. It affects your blood's ability to clot. If your blood doesn't clot, you can have heavy, hard-to-stop bleeding after an injury. The bleeding can damage your internal organs or even cause death, although this is rare.
In VWD, you either have low levels of a certain protein in your blood, or the protein doesn't work the way it should. The protein is called von Willebrand factor, and it helps the blood clot.