We encountered two patients with mediastinal parathyroid cysts. Patients 1 was a 44-year-old man with no complaints who had an abnormal shadow on a roentgenogram of the chest. An iperation was performed because a computed tomogram and a magnetic resonance image showed a cyst in the upper right part of the mediastinum, which was suspected to be a mediastinal thyroid cyst. Patient 2 was a 77-year-old woman with no complaints who had an abnormal shadow on a roentgenogram of the chest. Therapeutic thoracoscopy was performed because a mediastinal cyst was suspected based on the results of computed tomography and magnetic resonance image. Both patients had thin-walled that they were mediastinal parathyroid cysts. Mediastinal parathyroid cysts are very rare. We searched the medical literature but found previously published reports of only 39 cases.