Background <p>Brown tumors are rare non-neoplastic bone lesions associated with hyperparathyroidism. They are uncommon in the jaws and are usually linked to primary or secondary hyperparathyroidism, while tertiary hyperparathyroidism is rarely reported, particularly in normocalcemic patients. This report aims to present a mandibular brown tumor in a patient with long-standing renal disease and normocalcemia, and to discuss the diagnostic challenges between secondary and tertiary hyperparathyroidism.</p> Case presentation <p>A 41-year-old male on chronic hemodialysis with a history of parathyroidectomy presented with mobility of the mandibular second molar and vestibular swelling. Imaging revealed a radiolucent mandibular lesion, while histology showed multinucleated giant cells in a fibrous stroma consistent with a brown tumor. Biochemistry demonstrated persistently elevated parathyroid hormone (4868 pg/ml) with normocalcemia and hyperphosphatemia. Whole-body bone scintigraphy showed diffuse skeletal uptake, and 18&#xa0;F-fluorocholine PET-CT revealed parathyroid adenomas. The patient underwent a second parathyroidectomy with partial reduction of PTH levels, followed by calcimimetic therapy. The mandibular lesion showed signs of regression at follow-up, although parathormone levels remained inappropriately high.</p> Conclusion <p>This case highlights the diagnostic ambiguity between refractory secondary and normocalcemic tertiary hyperparathyroidism in dialysis patients. It underscores the importance of considering hyperparathyroidism in the differential diagnosis of jaw giant cell lesions, the need for multidisciplinary management, and the lack of clear surgical criteria in normocalcemic cases.</p>