Thromboangiitis obliterans (TAO), or Buerger's disease, is a segmental occlusive inflammatory disorder of the arteries and veins, and etiopathogenesis is still obscure. In the present study we investigated the prevalence of prothrombin 20210 G-->A, factor V 1691 G-->A (Factor V Leiden), and factor V 4070 A-->G (His 1299 Arg) mutations, found to be associated with increased risk for vascular thrombosis, in 36 patients with TAO. We performed a case-control study of these mutations. The odds ratio for prothrombin 20210 A allele compared with G allele was 7.98 (95% confidence intervals 2. 45-25.93). Only this prothrombotic genetic factor was associated with the risk of TAO (p=0.032). In conclusion, carrying the prothrombin 20210 G-->A may be an important prothrombotic risk factor of TAO. This genetic predisposition must be screened in these patients routinely, and clinical importance must be supported by further investigations.