While liposarcoma is the most common malignant mesenchymal neoplasm in adults, a mediastinal position is rare. We describe here the case of a 74-year-old female with an hourglass-shaped mass in the posterior mediastinum, which was probably present on a roentgenogram 4 years earlier. On a CT scan of the chest, the mass appeared non-homogeneous with a mainly adipose content. A preoperative ultrasonically guided tru-cut transthoracic biopsy revealed the presence of adipose tissue with mildly atypical cytological features. The mass was therefore completely excised by means of a right thoracotomy. The postoperative course was uneventful and the patient is alive and well and has had no recurrence in the 6 months since surgery. We review here the natural history, pathology, and prognosis of the disease, and discuss methods of diagnosis and management of such lesions.