This study will focus on patients having inferior vena cava (IVC) thrombosis, either with or without thrombosis in other veins.

The purpose of this study is to assess risk factors, safety and effectiveness of treatment options, and outcomes of patients with IVC thrombosis.

Thrombosis of the inferior vena cava (IVC) is a rare form of deep venous thrombosis (DVT). Optimal treatment strategies and clinical outcomes are not well established.

This multicenter, international, observational study will assess the effectiveness and safety of current treatment options in patients with IVC thrombosis, and describe the long-term outcomes of patients with IVC thrombosis.

Patients with an objective diagnosis of IVC thrombosis, either with or without proximal lower extremity DVT will be included. Information will be collected on baseline characteristics, risk factors for thrombosis, symptoms, mode of diagnosis, presence of concomitant lower limb DVT, PE, IVC filter or unusual site thrombosis (splanchnic, gonadal and renal veins), treatment modalities (anticoagulation and/or thrombolysis), choice of anticoagulant, dose and duration of treatment, recanalization assessment (if available), recurrence of VTE during follow up, bleeding according to International Society on Thrombosis and Haemostasis criteria, development post-thrombotic syndrome (PTS) according to Villalta score and mortality during follow up. Patients should be followed up for 24 months from diagnosis. The number of visits is left to the discretion of the treating physician, but information on clinical outcomes at two intermediate time points is requested.

Inclusion criteria:

1. Consecutive adult patients (> 18 years) with an objective diagnosis of IVC thrombosis, either with or without proximal lower extremity DVT (involving the femoral, common femoral, or iliac veins) will be eligible for the study.
2. Diagnosis should be obtained by either doppler ultrasonography, CT angiography or MRI angiography.
3. Patients who had objective diagnosis of IVC thrombosis within 6 months prior to the starting of the registry will also be eligible, providing they are prospectively followed up by the participating centers and all requested information is available.

Exclusion criteria:

Patients enrolled in interventional studies.

Patients with an objective diagnosis of IVC thrombosis, either with or without proximal lower extremity DVT