We describe a mediastinal myxoid liposarcoma case in a 47-year-old woman who complained of dyspnea. This kind of tumor is rare and becomes symptomatic by compression on mediastinal structures, especially on the respiratory tract. These neoplasms are therefore often voluminous at the time the diagnosis is made. Histopathologic examination is always necessary as much for diagnosis as prognosis. Surgery, whether radical or palliative, obtain the best therapeutic survival results in myxoid liposarcoma of the mediastinum.