A case report of a leiomyoma of the chest wall is presented. So far as we examined, this is the first case of the leiomyoma of the chest wall in Japan. A 40-year-old woman was admitted to our hospital because of an abnormal shadow in the right upper lung area in a chest X-ray film. The thoracic CT and MRI demonstrated a tumor of the chest wall projecting into the thoracic cavity. The tumor was excised. Histological examination indicated that the tumor was a benign leiomyoma. This tumor seems to originate from the wall of the small vessels histologically. The patient's postoperative course is uneventful.