Patients with proven recurrent venous or arterial thrombosis should be investigated for a predisposing cause corresponding to a hypercoagulable state. The latter is made up of two broad categories: the first consists of inherited thrombotic disorders; the second of a heterogeneous array of acquired clinical disorders, some of which are illustrated by clinical reports encountered in our department of internal medicine. Although the development and application of specific tests have provided valuable information about the pathogenesis of intravascular thromboses, these assays are currently able to provide aetiological diagnoses in fewer than 20 percent of young patients with recurrent venous thromboembolism.