Haemophilia is a rare bleeding disorder, characterized by factor VIII (HA) or factor IX (HB) deficiency. The absence or the reduction of fVIII or fIX result in impaired thrombin generation and clot formation, causing excessive bleeding (mainly haemarthrosis). Osteoporosis is a systemic bone disease characterized by a low bone mineral density (BMD). A decrease of mean BMD has been described in haemophilic patients compared to healthy controls in several studies. So, osteoporosis could be an underestimated haemophilia-related comorbidity. None of the following risk factors (reduced physical activity, joint damage, vitamin D deficiency and /or hepatitis C virus (HCV) infection) has been retained as a cause of osteoporosis in haemophilic patients. Another hypothesis is that bone loss could be directly linked to fVIII or fIX and/or thrombin deficiency. The aim of this study is to evaluate the prevalence of the bone loss in HA and B patients, according to the type, the severity and the presence (or not) of a prophylactic treatment (depending on the age at which it was began) and to compare it to a control population. The investigators will also evaluate the relation between BMD and FVIII, fIX and thrombin potential.