Patients with neurofibromatosis type 1 develop both benign and malignant tumors at an increased frequency. Most of the malignant peripheral nerve sheath tumors (MPNSTs) are considered as high-grade sarcomas originating from tissues of mesenchymal origin. It is generally accepted that MPNSTs occur in about 2% to 5% of neurofibromatosis patients. In this paper, we present a 16-year-old male patient with neurofibromatosis who developed MPNST of the retromolar area. The mass enlarged rapidly in a period of 6 weeks. The patient was treated surgically, and a tumor mass with a diameter of 7 × 6 × 4 cm was excised, but after 8 months a recurrence was observed at the same site. The sarcomatous change in a neurofibroma has an extremely poor prognosis, so patients with neurofibromatosis should be closely monitored for a possible malignancy. A rapid change in size of a preexisting neurofibroma, infiltration of the adjacent structures, intralesional hemorrhage, and pain indicate a possible malignant transformation to MPNST.