A patient with long-standing, asymptomatic, primary hyperparathyroidism developed pain in the anterior neck area, with cough, dysphagia and increasing shortness of breath. This led to respiratory insufficiency, which required endotracheal intubation and respirator assistance. During the ensuing hours the patient developed an area of ecchymosis on the anterior chest. Chest x-ray showed widening of the superior mediastinum, and CT scan showed a large mass with a fluid level. Surgery revealed a large hematoma originating from a mediastinal parathyroid adenoma with a hemorrhagic infarct. Serum calcium, previously elevated, decreased to normal with the onset of neck pain, and the patient remains normocalcemic. Previous reported cases of this rare complication of parathyroid adenomas are reviewed. Hemorrhagic infarct of a parathyroid adenoma may present with a rapidly enlarging mediastinal mass, and/or hypercalcemic crisis. Surgical removal of the infarcted adenoma can return the serum calcium to normal.