Introduction: Brown tumors, also known as osteitis fibrosa cystica, are focal bone lesions resulting from increased osteoclastic activity and fibroblastic proliferation. They represent a rare complication of uncontrolled hyperparathyroidism (HPT) and may affect any part of the skeleton, including craniofacial bones. Case: We report a case of a 31-year-old Malay female diagnosed with primary HPT secondary to multiglandular disease, who initially presented with symptomatic hypercalcemia. Biochemical evaluation revealed elevated corrected calcium (2.84 mmol/L; reference range 2.2–2.6 mmol/L), low phosphate (0.63 mmol/L; reference range 0.8–1.6 mmol/L), and markedly elevated serum intact parathyroid hormone (iPTH) (286 pg/mL; reference range 14.9–56.9 pg/mL). Ultrasound parathyroid showed a large right extrathyroidal lesion, most likely suggestive of parathyroid adenoma, where sestamibi scan suggested multiglandular parathyroid adenomas with possible mediastinal involvement. She underwent exploratory parathyroidectomy on 19 June 2024, with excision of bilateral inferior parathyroid adenomas confirmed on histopathology. Despite surgery, she had persistent hypercalcemia (2.8–3.1 mmol/L) and rising iPTH levels (307 pg/mL on 24 June 2024, increasing to 413 pg/mL by 2 September 2024), consistent with persistent disease. Repeat imaging demonstrated hyperfunctioning parathyroid tissue in the anterior mediastinum. Subsequently, the patient developed progressive enlargement of the left upper gingiva associated with significant pain during mastication. Clinical and radiological evaluation revealed aggressive lesions with cortical expansion. Excisional biopsy of the gingival lesion confirmed the diagnosis of brown tumors involving the jaws. She later underwent a second parathyroidectomy with intraoperative parathyroid hormone monitoring at another centre. Postoperatively, normalization of serum calcium and iPTH levels was achieved, which led to marked clinical improvement and regression of the craniofacial brown tumor. Conclusion This case highlights that skeletal manifestations of HPT, including brown tumors, may regress following adequate biochemical control without additional local therapy. Early recognition and definitive surgical management of persistent or ectopic hyperfunctioning parathyroid tissue are essential to prevent progression and promote spontaneous bone healing processes.