The annual incidence of venous thromboembolism (VTE) is about 1 to 2/1000 person-years and mortality is 10% when VTE occurs as pulmonary embolism. VTE is a multifactorial disease caused by hereditary and acquired risk factors. Among the latter, hormonal exposure in young women (estrogen-containing pill, pregnancy) remains a major health issue given the frequency of this condition and the 4 to 5-fold increased risk of VTE in the presence of such exposure. In practice, inherited thrombophilia screening is often performed with the aim to identify young women at higher risk for VTE and to avoid estrogen-containing pill or to reinforce thromboprophylaxis during pregnancy. The increased risk of thrombosis in relatives is incompletely explained by the presence of known thrombophilias, as the risk of thrombosis in first-degree relatives is increased even if patients do not have a detectable defect.8,9 In a large cross-sectional study including 2830 first-degree relatives of patients with VTE, we previously showed that the risk of VTE in the first-degree relatives of patients with a first VTE is strongly influenced by whether the VTE was provoked or unprovoked, the patient's age when the VTE occurred, and the number of relatives who have had thrombosis. The risk of VTE in first-degree relatives is about twice as high if the index case had an unprovoked compared to a provoked VTE, is about three times as high if the index case had VTE before about 50 years compared to later in life, and at least twice as high if two rather than one family members have had VTE. The influence of these factors on the risk of VTE in first-degree relatives was additive, and occurred independently of the presence of factor V Leiden or the prothrombin 20210A gene in index cases. The underlying hypothesis is that patients who have unprovoked VTE or at a young age often have undetected hereditary thrombophilias and that these defects increase the risk of thrombosis in their relatives. However, the number of included young women in the study was to low to confirm if such familial risk was also elevated if young women were on hormonal exposure.