Malignant peripheral nerve sheath tumor (MPNST) is defined as any malignant tumor arising from or differentiating toward the cells of the peripheral nerve sheath. MPNST accounts for about 5-10% of all soft tissue tumors and is often associated with neurofibromatosis type I (NF-1, von Recklinghausen's disease). It is one of the malignant tumors associated with von Recklinghausen's disease. Its common site is the lower and upper extremities, trunk, head and neck. But intrathoracic manifestations are very rare. We report a case of a 40 year-old man with multiple neurofibromatosis who was presented with an intrathoracic malignant peripheral nerve sheath tumor.