Primary hyperparathyroidism secondary to ectopic parathyroid (in anterior mediastinum) is rare in children. We report the case of a 12-year-old girl with a history of multiple fractures, renal calculi and limb deformities. She was diagnosed with hyperparathyroidism secondary to an intrathymic parathyroid adenoma. Sestamibi scan showed a lesion in the anterior mediastinum. A biochemical evaluation revealed hypercalcaemia, elevated alkaline phosphatase and parathormone levels. The lesion was marked with radioisotope and confirmed intraoperatively using a gamma camera. The child underwent thoracoscopic left thymectomy with the adenoma. Immediate decrease in calcium and parathyroid hormone values were noted intraoperatively and serial monitoring showed a downward trend. On follow-up, the child is doing well. Ectopic parathyroid adenoma is very rare. CT with radioisotope scans is helpful in diagnosis. Thoracoscopic excision of ectopic adenoma is safe in children.