The brown tumour of hyperparathyroidism is a localized bone tumour and an uncommon manifestation of hyperparathyroidism. A 27-year-old woman presented with a mandibular 8 × 10 cm solid mass diagnosed as central giant cell granuloma. Chemical blood analysis revealed increased serum calcium levels of 12.46 mg/dL and the parathyroid hormone level was 124 pg/dL. The patient underwent surgery with removal of a parathyroid mass. Histologically, this parathyroid tissue was seen to be limited by a fibrous capsule with morphological features consistent with atypical parathyroid adenoma. The mandibular tumour has receded and the patient declined further procedures. This is the first case reported of brown tumour as the primary manifestation of an atypical parathyroid adenoma, a lesion that shares some features with parathyroid carcinoma without the unequivocal properties of malignancy.