PURPOSE: To describe the CT findings of primary liposarcoma of the mediastinum, and to correlate these with the pathologic findings. MATERIALS AND METHODS: We retrospectively reviewed the medical records, chest radiographs and CT scans of four male patients with histopathologically proven primary liposarcoma of the mediastinum treated between September 1996 and April 2002. The CT scans were analyzed by two radiologists, and final decisions were reached by consensus. They were analysed in terms of tumor size and location, enhancement pattern, the pattern of the fat component, calcification, mass effect, pleural effusion, lymph node enlargement, pericardial effusion, tumor extension to the costophrenic junction, and adjacent organ invasion. RESULTS: All patients presented with dyspnea and chest pain. Pathologic subtypes, which were well-differentiated and pleomorphic, were myxoid (n=2) and mixed (n=2). The transverse diameter of the mass ranged from 10.5 to 21 cm. All tumors were located in the anterior mediastinum, and all had lobulated margins. Soft-tissue attenuation predominance (n=2) occurred in the myxoid type, and roughly equal amounts of fat and soft-tissue attenuation (n=2) were present in the mixed type. A small area at calcification was seen in the mixed type (n=1). Mass effect on mediastinal structures was demonstrated in all patients. In three patients, the tumor draped around and conformed to the shape of the costophrenic junction. Chest wall invasion occurred in one patient. CONCLUSION: Findings of an anterior mediastinal location, fat attenuation, mass effect, the invasion of adjacent organs, and a lobulated margin strongly suggested mediastinal liposarcoma. CT attenuation of the lesions correlated closely with the degree of histologic differentiation.