Brown tumor is an important but rare complication of primary hyperparathyroidism. It is seen in approximately 1% of the cases. Common involvement areas are long bones, ribs, hand, skull, pelvic bones, and mandible. The maxillary sinus is a rare involvement site. Patellar bone involvement has not been reported. Because brown tumor and giant cell tumor have similar histopathologic findings, the differential diagnosis is important. We present a patient with ectopic parathyroid adenoma with multiple brown tumors located in uncommon areas such as the maxillary sinus and patella. A 54-year-old female patient was operated on 3 times for the suspicion of osteal giant cell tumor. After admission, the diagnosis of primary hyperparathyroidism was suggested by the clinical history. This was confirmed by biochemical, radiologic, and histopathologic determinations. Excision of an ectopic parathyroid adenoma normalized the metabolic status. The unusual brown tumor localizations were important in the differential diagnosis of lytic skeletal lesions.