Several inherited polymorphisms are associated with risk of venous thrombosis, including Mutation at codon 506 of the factor V gene, mutation at position 20210 of the prothrombin gene, and mutations in the protein C gene. In this study, genotyping for factor V, prothrombin, and protein C Mutations was performed in 50 patients and 25 control Subjects by polymerase chain reaction-based analysis. The prevalence of factor V and prothrombin mutations was not significantly different from that in the general population. Nine Of the patients had heterozygous protein C mutation. There was a high prevalence of the Mutated protein C allele in the Pulmonary emboli group (42.8%). Protein C mutation incidence was higher in the pulmonary emboli group than in the deep vein thrombosis (8.33%) and cerebral vein thrombosis (16.1%) groups. These results indicate that patients with protein C deficiency have a greater risk of thrombosis than patients with factor V or prothrombin G20210A mutation.