SummaryConstitutional disturbances of the«prothrombin complex»concern the coagulation factors II, V, VII and X. A congenital deficiency of one of these clotting factors is rare and seldom total. The partial decreased level of one of the factors involved has a limited influence on the overall or globalin vitrocoagulation tests although the haemorrhagic syndrome might be evident. More specific tests have to be performed to diagnose correctly these unusual blood disorders and require the help of a specialised laboratory.A congenital deficiency of one component of the«prothrombin complex»follows an autosomal recessive hereditary pattern. This explains why the disease is apparently rare and overt in homozygotes only, and provided the abnormal gene has a high penetration. As hétérozygotes have only a minor deficiency, thev are not afflicted with bleeding and these individuals are usually not detected by the routine tests in blood coagulation.