Inherited thrombophilia is associated with an increased risk of thrombosis. Classically it consists of protein C and protein S deficiency, activated protein C resistance and antithrombin III deficiency. In pregnancy, in addition to thrombosis, inherited thrombophilia is associated with poor obstetric outcome, including recurrent miscarriage, late fetal loss, abruption and pre-eclampsia.Hyperhomocysteinaemia is a newly recognized cause of familial thrombophilia. It is likely that further causes such as prothrombin gene mutations will be added to the rapidly expanding list. The diagnosis of some forms of genetic thrombophilia must, however, be approached with caution during pregnancy, particularly protein S deficiency and activated protein C resistance.