Primary hyperparathyroidism (PHPT) in children and adolescents is a rare condition. PHPT is usually sporadic and caused by parathyroid adenoma. Patients may present with bone pain, proximal myopathy, bony deformities, fractures, renal calculi, mass on the neck, or acute pancreatitis. A sixteen-year-old boy presented to our outpatient clinic with difficulty in walking due to swelling of both ankles. Ultrasonography revealed intratendinous calcific nodules in both Achilles tendons. Serum biochemistry showed hypercalcemia and hypophosphatemia. Serum parathormone level was high (512 pg/mL). Parathyroid scanning revealed a suspected parathyroid adenoma. The patient underwent parathyroidectomy and the diagnosis of parathyroid adenoma was confirmed by histopathology. Serum levels of parathyroid hormone, phosphate, and calcium returned to normal, and the tenderness over the Achilles tendon and the flow pattern on Doppler examination disappeared as well. In conclusion, hyperparathyroidism should be kept in mind in the differential diagnosis of tendonopathies. Early diagnosis can be crucial for prevention of severe complications.