A 70-year-old man without any underlying disease was admitted to our hospital complaining of abdominal discomfort for 3 months. He denied alcohol consumption but was a current smoker with 20 pack-year history of smoking. His physical examination revealed grossly engorged and tortuous veins of the abdominal wall (Fig. 1A) and mild scleral icterus. His laboratory findings revealed the following: total bilirubin level of 3.68 mg/dL, prothrombin time of 14.8 seconds, and platelet count of 96,000/µL. Abdominal computed tomography demonstrated a massive thrombus in the inferior vena cava (IVC) with prominent proliferation of collateral vessels and subcutaneous collaterals (Fig. 1B and 1C). The liver was enhanced heterogeneously with multiple regenerative nodules. Further investigations were completed to detect the cause of thrombosis of the IVC, but no cause was found. Thus, a diagnosis of idiopathic Budd-Chiari syndrome (BCS) with thrombosis of the IVC was established. The patient received anticoagulation therapy with rivaroxaban. The abdominal wall varices had improved markedly 6 months after therapy (Fig. 1D).