An unusual case of a primary leiomyosarcoma of the chest wall is presented. The patient was a 41-year-old man and had no symptoms. The chest x-ray showed a tumor with mediastinal involvement. A percutaneous needle biopsy indicated that it was histologically a leiomyosarcoma. Wide en bloc excision of the chest wall was done, including much of the third, fourth and fifth ribs and a piece of lung. The defect was closed with GORE-TEX soft tissue patch. There were three courses of chemotherapy added, but the patient had a local recurrence, which was resected again, two years after the first surgery. It may be thought that wide en bloc excision and closely follow-up are important in the management of a leiomyosarcoma of the chest wall because of its high recurrence rate.