This observational study aims to establish a prospective nationwide cohort of venous thromboembolism. The main questions it mains to answer are:

• Which patients with venous thromboembolism should accept long-term anticoagulation therapy?
• Mechanism and prognosis of venous thromboembolism. Participants will receive yearly follow-ups through telephone, hospitalization, or outpatient care.

Venous thromboembolism (VTE), including deep venous thrombosis and pulmonary embolism, is a class of diseases with strong occultation, high mortality, and a high recurrence rate.Long-term anticoagulant therapy can reduce the risk of recurrence. Although long-term anticoagulation can reduce the risk of VTE recurrence, it will also increase the risk of major bleeding and the economic burden of long-term anticoagulation. Therefore, stratifying the risk of VTE recurrence and preventing recurrence with accurate anticoagulant therapy is an urgent problem in VTE management.

Investigators will establish a prospective nationwide cohort of VTE, develop a unified follow-up plan, and conduct whole-life follow-up management for patients. Demographic, clinical, imaging, laboratory indicators, gene, and other information of patients will be collected. A VTE patient database with complete clinical phenotype data, genetic data, and biological samples will be established.

Investigators will construct a VTE recurrence risk prediction model based on Chinese data to provide clinical decision suggestions for clinicians to select appropriate individualized anticoagulant duration according to risk stratification. VTE patients with low recurrence risk could avoid long-term anticoagulant therapy.

Inclusion Criteria:

• Age greater or equal to 18.
• Patients diagnosed with venous thromboembolism.

Exclusion Criteria:

• Pregnant or lactating women
• Patients with active tumor

Consecutive patients diagnosed with venous thromboembolism will be eligible to participate in the study.