Our objective is to provide a contemporary assessment of VTE risk in adults with: Factor V Leiden mutation (hetero- and homozygous), prothrombin G20210A mutation (hetero- and homozygous), Factor V Leiden and prothrombin compound heterozygosity, and natural anticoagulant deficiency (protein S, protein C, and antithrombin deficiency). The gene discussed is F5; the disease is hereditary antithrombin deficiency.