Giant cell lesions of the mandible, though uncommon, can be the presenting sign of HPT. Hyperparathyroidism causes an imbalance of osteoclastic and osteoblastic activity, leading to focal areas of bone resorption. Fibrous replacement of bone marrow and microhemorrhage result in a brownish mass known as brown tumor. Before the advent of inexpensive assays for calcium and phosphorus in the 1950s and 1960s, brown tumors were commonly seen as the presenting symptom of HPT.1 Today, with widespread screening for calcium and phosphorus abnormalities, as well as parathyroid hormone, most cases of HPT are detected in asymptomatic patients. Some patients who do not undergo routine laboratory screening, however, may develop brown tumors.