Thromboangiitis obliterans, or Buerger's disease, is a segmental occlusive inflammatory disorder of the arteries and veins most commonly affecting the lower extremities of young male cigarette smokers. The etiopathogenesis of the thromboangiitis obliterans is still obscure. The authors have identified heterozygosity for the recently described prothrombin gene 20210 G-->A variation and Factor V Arg 506 to Gln (Factor V Leiden) mutation in a patient with Buerger's disease. Both mutations confer a high risk of thrombosis. This coincidental observation may serve as further evidence that a thrombotic mechanism is involved in Buerger's disease.