A 26-year-old man presented with shortness of breath on exertion that was gradually getting worse. His history revealed a mass in the left hemithorax that had been growing on follow-ups. Physical examination only showed that the respiratory sounds were fainter on the left. Thoracic computerized tomography was performed to elucidate the left hemithorax lesion seen on chest x-ray and a giant mass of lipid density extending from the anterior mediastinum to the diaphragm and filling almost the entire left hemithorax was observed. Total excision of the 25 x 21 x 8 cm mass weighing 1580 g was performed with a left thoracotomy. The histopathology investigation of the mass was reported as thymolipoma. The case was presented because it is a rare mediastinal mass.