Tuesday, 11 September 2012, 09.30 -10.30 Objective: Liposarcoma is the most commonly diagnosed soft tissue sarcoma in adults and occurs predominantly in the lower limbs and retroperitoneum. Primary mediastinal liposarcomas are rare accounting for less than 1 % of all mediastinal tumors. Method: We report a retrospective study of 4 cases of mediastinal liposarcoma during an 8-year period. Diagnosis was made on mediastinal biopsy in 2 cases and on resected specimen in the 2 other cases. Results: There were 3 men and a women ranging in age from 28 to 81 years, explored for respiratory symptoms. Radiological findings showed an anterior inhomogeneous mediastinal mass in all cases with extension to left hemithorax in one case. A surgical resection was achieved in only 2 cases but was incomplete. Histopathologically, tumors were classified into 2 well differentiated lipoma-like liposarcoma, one myxoid liposarcoma and one mixed liposarcoma (sclerosing liposarcoma with myxoid liposarcoma). All patients received adjuvant radio or chemotherapy. One of them presented lung metastasis during the follow up and another died from respiratory failure. The two other are still alive. Conclusion: Mediastinal liposarcomas include a heterogeneous group of bulky tumours, the progression of which depends on the histological type. Histopathologic examination is always necessary as much for diagnosis as prognosis.