We experienced a rare case of a 76-year-old man with an anterior mediastinal tumor diagnosed postoperatively as atypical thymic carcinoid with hypercalcemia. He was found to have a growing abnormal mediastinal shadow, and admitted. Chest computed tomography scan on admission revealed an anterior mediastinal mass of 4.0 cm in diameter. Extended total thymectomy was performed through a median sternotomy. The histopathological diagnosis was an atypical carcinoid of the thymus. He received adjuvant mediastinal irradiation. Endocrinological tests for preoperative hypercalcemia revealed high levels of serum intact-parathyroid hormone( PTH), prolactin and gastrin. A parathyroid scintigraphy revealed a parathyroid tumor. He has been well without any sign of recurrence for 1 year after surgery and irradiation treatment. When diagnosing anterior mediastinal tumor with hypercalcemia, atypical carcinoid of thymus with hyperparathyroidism should be considered.