 Brown tumor, BT, is the pathological expression of osteitis fibrosis cystica owing to primary and secondary hyperparathyroidism, HPT. It is a rare benign lesion of skeletal system that usually affects the facial bones, clavicles, ribs, pelvis, and extremities. The purpose of this case report is to present the clinical, pathological, and radiological findings of BT, rarely seen in adults, originating from the giant parathyroid adenoma and emerging as the first clinical sign of HPT. The patient underwent a successful parathyroidectomy operation and on the first post-operative day, the patient was discharged without any complications. Continuous. This article was authored by Banu Yajit, Murtanel, and Bülent Sitches.