Parathyroid carcinomas are rare endocrine tumors which comprise 0.3-5.6% of all causes of hyperparathyroidism. 90% of them are hormonally active, while 10% of them may be non-functional. They mostly occur in a single parathyroid gland. Concurrent involvement of both parathyroid glands is quite rare. A 57-year-old male patient was admitted to emergency department with the complaint of dyspnea. Thorax tomography revealed a retrosternal mass. The mass was thoracoscopically excised by thoracic surgeons. Histopathological examination result of the mass was reported as parathyroid carcinoma. Parathyroid scintigraphy performed and focal activity increase in the lower pole of the left lobe. Parathyroid hormone level was 118 pg/ml and calcium level was measured as 11.4 mg/dl. The patient with these findings was operated and pathological examination of excised left lower parathyroid tissue was reported as carcinoma. In addition, micropapillary carcinoma was detected in left thyroid lobectomy specimen. Our case was also unusual in that double parathyroid carcinoma, which is a rare condition, was hormonally inactive. We aimed to present our case in the light of the literature due to its rare occurrence.