Hageman factor deficiency, also known as factor XII deficiency, is a rare genetic blood disorder that causes prolonged clotting (coagulation) of blood in a test tube without the presence of prolonged clinical bleeding tendencies. It is caused by a deficiency of the Hageman factor (factor XII), a plasma protein (glycoprotein). Although it is thought that factor XII is needed for blood clotting, when it is deficient, other blood clotting factors tend to compensate for its absence.

This disorder is thought to be benign and usually presents no symptoms (asymptomatic); it is usually only accidentally discovered through pre-operative blood tests that are required by hospitals. Of substantial recent interest is the role of antibodies to Factor XII in recurrent pregnancy losses.