The aim of this study was to investigate the hereditary thrombophilic risk factors in patients with venous thromboembolism (NIT E) and whether these risk factors play a different role in patients with isolated pulmonary embolism (PE) as compared with patients with deep vein thrombosis (DVT) and patients with PE + DVT. The protein C (PC), protein S, antithrombin activities, homocysteine levels, and factor V Leiden (FVL) G 169 1A and prothrombin G20210A mutations were evaluated in 191 patients with VTE and 191 controls. The prevalence of FVL and PC deficiency were higher in patients (P =.003 and P =.02, respectively). There was no significant difference for the other risk factors. The combination of thrombophilic risk factors was significantly higher in patients with DVT + PE as compared with patients with isolated PE or DVT (P =.04). In conclusion, the most important hereditary risk factors for VTE in this study were the FVL mutation and PC deficiency.