A 73-year-old man underwent splenectomy for treatment of chronic idiopathic thrombocytopenic purpura (ITP), but platelet count decreased again. An infrarenal abdominal aortic aneurysm (AAA) with a diameter of 3.9cm had been pointed out at splenectomy. Because follow up CT showed the diameter of the AAA to exceed 5cm, Y-graft replacement of the infrarenal AAA was performed following preoperative immunoglobulin infusion therapy. A year later he suffered from deep vein thrombosis in his left leg. Although platelet count decreases in patiens with ITP, platelet aggregation may increase. We must be aware of the possibility of the occurrence of venous thromboembolism.