We report a case of spontaneous parathyroid adenoma hemorrhage. A 50-year-old man with a sore throat, and swelling and ecchymosis of the entire anterior neck was found in cervical and chest computed tomography revealed to have a low-density area extending from the parapharyngeal region to below the carina, Suspecting descending necrotizing mediastinitis secondary to a peritonsillar abscess, we conducted mediastinal and cervical drainage, but found no abscess. No evidence was found, either, in bacteriological culture of sputum and pleural effusion. After the hematoma disappeared, cervical ultrasonography indicated parathyroid adenoma. Serum calcium was marginally increased, indicating that serum calcium should be determined if cervical or mediastinal hematoma develops without an obvious cause.