Ossifying fibroma is an uncommon benign osteogenic neoplasm arising from cells of the periodontal ligament, typically with a slowly progressive enlargement of the affected bone. The neoplasm sometimes presents with hyperparathyroidism, most of which cases are due to familial parathyroid tumours. We report a rare case of ossifying fibroma of the mandible which showed very rapid growth and presented with primary hyperparathyroidism due to non-familial parathyroid adenoma. Despite improvement of parathyroid dysfunction after removal of the parathyroid adenoma, the tumour continued to grow very aggressively. The case required partial mandibular resection for complete resection of the tumour, and fixation of the remaining mandible with a titanium plate.