We report a case of intrathoracic malignant peripheral nerve sheath tumor in a 65-year old woman revealed after a few-month history of progressive dyspnea, appetite and body mass loss. The chest magnetic resonance (MR) examination revealed the presence of a large tumor occupying the mediastinum and a major portion of the right hemithorax. The diagnostic tumor sample was obtained by parasternal biopsy in local anesthesia. The surgical resection of the tumor could not be performed due to its excessive size, intrathoracic involvement and bad respiratory reserves of a patient. The chemotherapy and irradiation were performed as palliative measures. The lethal outcome appeared 10 months after the diagnosis was established.