Diagnosis and treatment of ectopic parathyroid adenoma are challenging. Herein, we report the cases of two male patients who had ectopic parathyroid adenomas located in the thymus. Both the patients had recurrent kidney stones and life-threatening hypercalcemia. Their parathyroid adenomas were localized through preoperative Tc-99m sestamibi scanning and successfully resected through unilateral neck exploration. Primary hyperparathyroidism can be overlooked inpatients with recurrent kidney stones or refractory cardiovascular diseases. Preoperative imaging studies, such as Tc-99m sestamibi scanning, can localize ectopic parathyroid adenoma and facilitate a successful and minimally invasive parathyroidectomy.