Parathyroid adenomas sometimes cause nephrolithiases or bone disorders, but most cases pass subclinical courses and are found incidentally by routine blood tests. We report a case of parathyroid adenoma causing posterior mediastinal hemorrhage. The parathyroid adenoma was excised five months subsequent to the hemorrhage, after the hematoma had efficiently subsided, with no major bleeding. The postoperative course was uneventful with an expected decrease in serum calcium and intact PTH.