We encountered an unusual case of hyperparathyroidism with both hemosiderin deposits on the ribs and low intensity on T2-weighted magnetic resonance imaging (MRI) caused by a parathyroid adenoma with multiple brown tumors that mimicked metastatic bone tumor due to false positive results on computed tomography (CT) and Tc-99m sestamibi (MIBI) imaging. The patient, a middle-aged woman, had very high serum levels of calcium (14.1 mg/dl), alkaline phosphatase (9,369 IU/l) and intact-PTH (12,400 pg/ml), and a large tumor (2.5 cm in diameter) in the lower portion of the left lobe of the thyroid. Plain X-ray revealed a soft tumor in the left chest wall. On CT scan, there were multiple destructive masses in the ribs, including large intramedullary masses on both 3rd ribs. On MIBI scintigraphy, there was strong late uptake in the lower portion of the left cervical region, both 3rd ribs, and the left 7th, 8th, and 10th ribs. T2-weighted image MRI scans showed that both 3rd ribs had a low intensity with hemosiderin deposits. These findings suggested that the patient had hyperparathyroidism with multiple bone metastases due to carcinoma of the parathyroid gland. However, on pathology, the resected tumor of lower portion of the left lobe of thyroid was diagnosed as a parathyroid adenoma, and the tumors of the left 3rd and 7th ribs, as well as the right 2nd rib, were shown to be brown tumors. After resection, the patient's serum levels of calcium, alkaline phosphatase, and intact-PTH normalized. At 1.5-years follow-up, CT, MIBI, and MRI scans showed no abnormal findings. It is necessary to determine whether MRI can be used to distinguish between brown tumors and metastases caused by carcinoma of the parathyroid gland.