A 41-year-old woman presented with severe and sudden anterior neck swelling, pain, and dysphagia. Computed tomography (CT) scan and ultrasound of the neck showed a giant mass in the retropharyngeal space, displacing the trachea and esophagus anteriorly. Aspiration cytology was done, following which extensive cervical and chest ecchymosis occurred and her symptoms immediately improved. A repeat CT scan demonstrated that the cervical giant mass had vanished, but there was a residual mass in the left paratracheal space. Exploratory surgery of the neck revealed a parathyroid cyst with severe adhesion to the surrounding tissues. We considered that a ruptured parathyroid cyst had induced massive hemorrhage into the cervical tissues and mediastinum, but that the hemorrhage had been absorbed. Extracapsular hemorrhage from a parathyroid adenoma or cyst is rare, especially from a parathyroid cyst. In fact, to our knowledge, this represents only the third case of symptomatic spontaneous bleeding of a parathyroid cyst. Nevertheless, this entity should still be considered in the differential diagnosis of all rapidly progressing retropharyngeal masses.