Primary intra-osseous squamous cell carcinoma (PIOSCC) is a rare tumour which occurs centrally within the jaws. It is believed to arise from odontogenic epithelial remnants or from pre-existing odontogenic cysts/tumours. A case of PIOSCC arising from an odontogenic cyst in a 57-year-old female is discussed. Initial clinical and radiographic examination was suggestive of an odontogenic cyst / cystic tumour. The lesion was enucleated and sent for diagnostic histopathology which revealed the presence of an invasive carcinoma arising from the walls of the odontogenic cyst. The patient then underwent right mandibular resection and reconstruction as well as right supra-omohyoid neck dissection. Long standing odontogenic cysts have the potential to undergo malignant transformation though this may not always be the case. Relying only on radiographic findings for the management of cyst-like lesions without obtaining histopathological diagnosis is extremely ill-advised.