An elderly lady was diagnosed with primary hyperparathyroidism after being admitted to hospital with pyelonephritis and constipation. A sestamibi parathyroid scan demonstrated increased uptake in the upper mediastinum, suggesting an ectopic mediastinal parathyroid adenoma. The 4-mm adenoma was successfully removed through a mini-sternotomy incision using a gamma probe to identify the gland from the surrounding tissue. The patient made an uneventful recovery.