Malignant peripheral nerve sheath tumours (MPNSTs) are a rare but aggressive form of soft tissue sarcoma with few reported cases in the anatomic location seen with the case presented here. This case involves a 23-year-old man presenting with a soft tissue mass under the mandible found to be a MPNST, which was investigated and fully excised. Adjuvant radiotherapy was used postoperatively. Although uncommon, these tumours have a poor prognosis and suitable management therefore needs to be put in place as soon as possible. Complete excision with negative margins and adjuvant radiotherapy are the current methods used for treatment. This case is unusual and highlights the management of an aggressive tumour in a difficult anatomical area, prompting the consideration of MPNST as a differential diagnosis for a soft tissue mass.