A 79-year-old man had a 3.5-year history of edema of the lower extremities of unknown etiology. Abdominal computed tomography showed a soft tissue mass around the abdominal aorta, and the biopsy revealed dense fibrosis with abundant infiltration of IgG4-positive plasma cells. His serum IgG4 level was increased to 188 mg/dL. His lower extremity edema was induced by stenosis of the inferior vena cava (IVC) due to the mass. With a diagnosis of IgG4-related retroperitoneal fibrosis, he was treated with steroid, and the leg edema decreased with improvement of patency of the IVC and reduction of the soft tissue mass.