Inherited thrombophilia is a genetic tendency to venous thromboembolism. Coagulation abnormalities are common in the general population and therefore will present spontaneously in some individuals. Patients with a family history of thrombosis are at an increased risk for a mutation. Factor V Leiden and the prothrombin, G20210A mutation the commonest inherited risk factors for thrombosis, are associated with an increased risk of venous thromboembolism. These causes of thrombophilia increase the risk of venous thromboembolism recurrence. Deficiencies in protein C, protein S, and antithrombin-Ill account for most of the remaining cases of thrombophilia. Inherited thrombophilia should be suspected in patients with one or more of the following clinical features: idiopathic thrombosis, thrombosis at a young age, recurrent thrombosis, and thrombosis at an unusual site. Reliable assays are now available to test for the presence of the various causes of inherited thrombophilia.