We herein on report a case of a resected thrombosed venous aneurysm in the external jugular vein of an 81-year-old woman who noticed swelling of a soft mass with no pain in the left side of her neck. Physical and computed tomography findings did not suggest a thrombosed venous aneurysm. However, at a 3-month follow-up, the woman complained of pain in the mass, and magnetic resonance imaging and ultrasonography findings suggested a thrombosed venous aneurysm. Complete surgical resection under general anesthesia was performed successfully with no complications. Histopathologically, the aneurysm had thrombosed. The postoperative course has remained uneventful. We consider a thrombosed venous aneurysm in the external jugular vein merits aggressive surgical indications. Even if a venous a neurysm is not thrombosed at the time of its identification, regular follow-up is important, taking the possibility of thrombus formation occurring in the future.