All patients over 16 years ago may be included in the program when CVT diagnosis is proved by magnetic resonance angiography (MRA). For each included patient, there are four blood assays: the first just at the time of diagnosis and before the beginning of treatment, the second before the beginning of the oral anticoagulant treatment. The third assay is done in the third month at the time of a MRA. The last assay is made one month after the end of the anticoagulant treatment or in 12th month after the beginning of the disease if the treatment goes on.