A 62-year-old Chinese man was found to have abnormalities during his laboratory examinations with elevated serum calcium (Ca) (4.08 mmol/L) and alkaline phosphatase (236 U/L) levels and decreased serum phosphorus (0.65 mmol/L) and urine calcium (U-Ca) (15.54 mmol/day) levels. The parathyroid hormone (PTH) level (172.00 pmol/L) was increased significantly. The thoracic magnetic resonance imaging (MRI) results suggested that there was a neoplastic lesion in the anterosuperior mediastinum. A whole-body bone scan indicated active bone metabolism. The patient’s bone density test results showed that the T scores of the lumbar vertebrae, the femoral neck, and the total hip were –2.0, –2.4, and –2.5, respectively. The patient had mild osteoporosis. The single photon emission computed tomography/computed tomography (SPECT/CT) results revealed that there was a hyperfunctioning ectopic parathyroid adenoma (Fig. 1). Afterwards, the patient underwent median sternotomy. The pathological results are presented in Fig. 2. The patient’s PTH, Ca, and U-Ca levels all returned to normal postoperatively. All the above findings confirmed a diagnosis of primary hyperparathyroidism due to an ectopic parathyroid adenoma.