Background and Objectives: HT is an important risk factor for venous thromboembolism, especially among patients without acquired risk factors. The aim of our study was to investigate prevalence and clinical features of HT in patients with idiopathic PTE in Korean population. Subjects and Methods: From October 2004 to January 2009, 316 patients with PTE diagnosed by CT scan were analyzed in this study. We excluded 153 patients (48%) with PTE associated with malignancy. We retrospectively reviewed 163 patients (52%) to investigate their clinical characteristics and laboratory tests for assessing thrombophilic status. We diagnosed HT with thrombotic profile tests and genetic tests. Results: In total 163 patients, 89 patients (55%) (group A) had no known acquired risk factors for venous thromboembolism and 74 patients (45%) (group B) had equal or more than one acquired risk factors except malignancy. In group A, thrombotic profile tests were performed in 54 patients (61%). By thrombotic profile tests, 15 patients (17%) in group A were diagnosed as strongly suspected HT and 16 patients (18%) as suspicious HT. When we compared these 31 patients (35% of group A) with patients of group B, they had younger age (46짹15 years vs. 61짹18 years, p<0.01) and higher rate of recurrence of venous thromboembolism at presentation (45.2% vs. 2.7%, p<0.01). Finally, 10 patients (11% of group A, age 44짹13 years) were confirmed with HT by genetic tests. Mutation analysis revealed protein C deficiency in 4, protein S deficiency in 3, AT-III deficiency in 2, and dysplasminogenemia in 1. Seven out of 10 patients had a history of recurrence of venous thromboembolism. Conclusion: We concluded that HT is not uncommon among patients with idiopathic PTE in Korea. Patients with PTE especially if younger and/or with a positive history of recurrence should be evaluated for the presence of HT.