The role of Factor V is to accelerate the activity of thrombin. When levels of Factor V are low, clotting is delayed or progresses slowly. People with this deficiency may have occasional nosebleeds, excessive menstrual bleeding, and bruising, although many have no symptoms. The first sign of this condition may be bleeding following surgery. The treatment is administration of fresh frozen plasma is not given because Factor V deteriorates rapidly.

Factor V deficiency has to be distinguished from a combined deficiency of Factors V and VIII, which is entirely separate disorder.