Mediastinal liposarcoma (ML) is a rare mesenchymal tumor, accounting for less than 1% of mediastinal tumors. They have a slow growth, so they may not give symptoms for a long time, until the tumor produces compression of close structures. The treatment of choice is surgery, which can be combined with chemo-radiotherapy. We present a case in which the diagnosis of a ML was made in a 30-year-old woman with dyspnea and chest pain.