Backgrounds: In some patients with pulmonary thromboembolism (PTE), classic risk factors such as cancer, major surgery, immobilization, delivery and estrogen supplement are not found. These patients are called unprovoked or spontaneous PTE. We tried to elucidate the clinical characteristics and prognosis of provoked and unprovoked PTE. Methods: We consecutively included 300 patients who had been hospitalized with acute PTE in a single center from 1998 to 2008. We classified the patients into 2 groups; provoked and unprovoked, based on whether the patients had had risk factors of PTE. We compared clinical characteristics (age, sex, BMI, hypertension, diabetes, creatinine, cholesterol, triglyceride, CRP, BNP, D-dimer, protein C, protein S and history of coronary artery disease (CAD) or cerebrovascular accident (CVA)) and mortality in both groups. Independent prognostic factors for composite end-points (death and recurrence) in unprovoked group were also analyzed by univariate and multivariate analysis. Results: The numbers of patients (mean age, 63.6 짹 15.0 years) in provoked and unprovoked group were 167 (55.7%) and 133 (44.3%), respectively. Mean follow-up period was 25.4 months. Unprovoked group had significantly more history of smoking (p = 0.045) and CAD (p = 0.027), and lesser history of CVA (p = 0.013) than provoked group. Provoked group had significantly higher mortality (p < 0.001) than unprovoked group. Non-cancer provoked group (n = 57) had still higher mortality (p = 0.024) (Figure). Independent prognostic factors for composite end-points in unprovoked PTE were higher level of creatinine (>1.2 mg/dL, p = 0.042, OR = 7.0), and CRP (> 3 mg/L, p = 0.042, OR = 3.9). Conclusions: Provoked PTE have poorer outcome than unproved PTE. Prognostic factors in unprovoked PTE were creatinine and CRP. Figure (A) Survival curves of provoked (dotted line) and unprovoked PTE (solid line), (B) non-cancer provoked (dotted line) and unprovoked PTE (solid line).