A case of primary hyperparathyroidism due to parathyroid adenoma is presented. A 14 year-old male was admitted to the hospital comptaining of voiding difficulty. The intravenous pyelogram demonstrated a stone in the proximal one third of the left ureter and marked hydronephrosis of the left kidney. The Tc-99m sestamibi nuclear scan demonstrated a hot spot below the lower pole of the left lobe of the thyroid. Laboratory study demonstrated hypercalcemia (12.4 mg/dL) and elevated parathyroid hormone (143.67 pg/mL). A parathyroid gland located below the lower pole of the left lobe of the thyroid was excised. A parathyroid adenoma, consisting of mainly chief cells was found on pathologic examination. Postoperatively the patient had transient hypocalcemic symptoms, which resolved with administration of calcium preparation and vitamin D.