The patient was a 63-year-old woman who sought medical care for her chief complaint of a cough. Chest CT scans revealed an 82 mm×47 mm tumor in the anterior mediastinum accompanied by bilateral multiple lung nodules. A diagnosis of leiomyosarcoma was reached for a nodule in the lingular segment, which was biopsied using thoracoscopy. We made a diagnosis of anterior mediastinal leiomyosarcoma with multiple metastases to the lung, since other primary lesions could be ruled out on the basis of FDG-PET. Treatment of stage IV soft-tissue sarcoma has not been standardized, and few reports are available concerning the efficacy of chemotherapy for advanced mediastinal leiomyosarcoma. This case was therefore treated with 8 courses of doxorubicin, based on past reports concerning the management of soft-tissue sarcoma. As a result, the patient is still alive after 18 months of doxorubicin therapy with an 11-month period of nonprogression.