We report a 66 years old woman with a diagnosis of primary hyperparathyroidism. Localization to mediastinum was obtained with parathyroid scintigraphy using 99mtc-methoxy-isobutyl-isonitrite (Tc99-MIBI). The patient was successfully operated upon by means of a videothora-coscopic approach. During the procedure serum parathormone was measured before and 10 minutes after adenomectomy, showing a more than 50% reduction from the basal level. An attempt to detect the precise site of the adenoma with a Tc99-MIBI probe was unsuccessful because of its proximity to the myocardium, but radioactivity was confirmed on the surgical specimen after resection. The patient's calcemia and parathormone levels became normal during the postoperative course and she remains normocalcemic 9 months after the procedure. In our case, preoperative localization and intraoperative parathormone measurements were both very useful for confirming surgical success; the intraoperative localization with a radioactive probe was not useful, but radioactivity was confirmed after resection on the surgical specimen. The endoscopic surgical procedure with videothoracoscopy was well tolerated, less painful than a thoracotomy, and it shortened the hospitalization period.