Myeloproliferative disorders are the main cause of Budd-Chiari syndrome in western countries. Inherited or acquired thrombophilic factors have also been implicated. A novel mutation of the prothrombin gene (G-->A20210) has only been described in a few cases of Budd-Chiari syndrome so far. Venous thrombosis is often the result of multiple concomitant thrombophilic factors. We report the case of a patient with essential thrombocythemia and Budd-Chiari syndrome in which heterozygosity for both factor V Leiden and the mutation G20210A of the prothrombin gene were identified.