The authors present a case of a 71-year-old woman with clinical and biochemical features of primary hyperparathyroidism and a history of right pneumonectomy. An ultrasound scan did not demonstrate any abnormality. A planar Tc-99m methoxyisobutylisonitrile (Tc-99m MIBI) scan showed an area of minimally increased uptake within the right hemithorax. However, unlike most adenomas, this demonstrated washout similar to the thyroid at 90 minutes and 3 hours. Subsequent SPECT imaging clearly showed the lesion in the superior right hemithorax. A CT scan and angiogram confirmed the presence of this mass. After surgery, histology confirmed the diagnosis of a parathyroid adenoma. Postoperatively, the calcium and PTH levels returned to normal.