One hundred and five cases of factor V inhibitors were published between 1955 and 1997. According to pathogenesis, factor V inhibitor patients can be divided into five groups: patients exposed to bovine thrombin; patients after surgery without exposure to bovine proteins; miscellaneous associated conditions; 'idiopathic' inhibitors; inhibitors in congenital factor V deficiency. The clinical and biochemical properties are described. The overall prognosis of factor V inhibitors is good, but there are differences among the five groups with the best prognosis in patients exposed to bovine thrombin and the worst prognosis in 'idiopathic' inhibitors. Only a few treatment options are available. Immunoadsorption and plasmapheresis seem to be the most effective methods for therapy of acute bleeding. Many inhibitors disappear spontaneously and it is uncertain whether an immunosuppressive treatment hastens the disappearance of the inhibitor.