In this issue of Blood, Holzhauer et al have determined a novel method of identifying patients with protein C, protein S, and antithrombin deficiency who are at increased risk of developing venous thromboembolism (VTE; see figure). Children with VTE and their relatives were screened for inherited thrombophilia including proteins C and S and antithrombin deficiency; and Factor (F)V G1691A and FII G20210A. Their study demonstrates that relatives with proteins C and S and antithrombin deficiency are at a significantly higher risk of developing VTE compared with those without inherited thrombophilia.