Herein we describe the case of an 81-year-old woman with an anterior mediastinal tumor. The tumor was initially discovered at the age of 62 during a workup (computed tomography [CT] scan) for aplastic anemia. At the age of 77, she was referred to our department due to the anterior mediastinal tumor. A repeat CT scan revealed no change in tumor size. Subsequently, another CT image examination revealed lung lesions contiguous with the anterior mediastinal tumor as well as swelling of a right paratracheal lymph node. We diagnosed it as lymphoepithelioma-like carcinoma (LELC) by transbronchial biopsy. Due to her advanced age, performance status 2, and chronic renal disease, we performed only radiation therapy (RT). To the best of our knowledge, no study has reported the use of RT alone for mediastinal LELC; therefore, we believe this case will be valuable in evaluating a clinical course and image findings.