Primary hyperparathyroidism is the main cause of hypercalcemia in ambulatory patients. Classic surgical resolution of this disease includes bilateral cervical exploration with exhibition of the four parathyroid glands and evaluation of the suspicious gland with a rapid biopsy. We report a 79 years old female with a primary hyperparathyroidism in whom the adenoma causing the disease was located with the help of an intraoperatory gamma-probe that detected the zone of higher radiation counting of Tc99m Sestamibi, that was injected preoperatively. The patient was discharged with normal serum calcium and phosphate levels (Rev Méd Chile 2001; 129: 921-4).