Rectal sheath hematoma has been a well-known clinical entity from the ruin of the ancient Greece. It is relatively rare, however, to encounter this abdominal disorder in the clinical setting. Furthermore, the initial symptoms of rectus sheath hematoma are often similar to those of acute abdominal disorders. Therefore, the majority of the patients with rectus sheath hematoma have been treated with operative procedures because of the difficulty of a differential diagnosis from other abdominal disorders. We recently treated a 74-year female diagnosed with rectus sheath hematoma with the anticoagulants after an episode of cerebral infarction. From the findings of the physical examinations, ultrasound, and computed tomography, we could correctly diagnose, and could treat her with completely conservative methods without any invasive techniques. It is stressed that it is important to recognize this entity of rectus sheath hematoma when patients are examined, after complaining of acute abdominal pain and with evidence abdominal masses in the clinical setting.