Primary mediastinal liposarcomas are extremely rare malignancies that remain asymptomatic until large and, even then, initial symptoms are nonspecific. We report a 48-year-old man followed up for asymptomatic multiple bullae who suffered progressive weight loss and dyspnea on exertion. Radiography and computed tomography of the chest showed a large mass with calcified nodules in the left pleural cavity and giant bullae in the right pleural cavity. Previous computed tomography of the chest showed a small tumor of mediastinal adipose tissue with calcified nodules. Tumor growth was calculated at about 500 times the tumor volume per 3.6 years. We completely resected the mediastinal tumor and conducted a bullectomy through a median sternotomy. The microscopic pathological diagnosis was well-differentiated/sclerosing liposarcoma. The man underwent no postoperative adjunctive irradiation and remains well 8 months after surgery.