We describe 17 cases (9 women, 8 men; aged 36 to 72 years) of primary parathyroid tumors occurring primarily in the anterior mediastinum. Clinically and radiologically, all patients had an anterior mediastinal tumor. All patients had metabolic disturbances with calcium and phosphorus. Of 17 patients, 13 had clinical primary hyperparathyroidism, 1 had secondary hyperparathyroidism due to polycystic kidney disease, and 1 had a history of prostatic carcinoma and 1 of chronic obstructive pulmonary disease. In 1 patient, the tumor was found at autopsy. Grossly, the tumors varied in size from 2 to 7 cm in greatest dimension. Histologically, 2 tumors showed features of parathyroid carcinoma, and 15 tumors showed more conventional features of parathyroid adenomas. Six tumors were predominantly oncocytic, 6 were composed predominantly of chief cells, and 3 had mixed cellular composition. Immunohistochemical studies for chromogranin, synaptophysin, low-molecular-weight keratin (CAM 5.2), and parathyroid hormone were performed in 10 cases (8 parathyroid adenomas and 2 parathyroid carcinomas). All the tumors examined showed variable positive reaction for those antibodies. The cases highlight the importance of keeping primary parathyroid tumors in the differential diagnosis of anterior mediastinal tumors.