Summary. A 70-year old female patient was admitted to the hospital because of scheduled thoracotomy and biopsy of poste- rior mediastinal retrocardiac tumor of unrecognized etiology. The patient had no complaints regarding the tumor. Routine anesthesiological preoperative examination revealed status ASA III. Induction in anesthesia was usually stable. At the moment when the surgeon intraoperatively touched the tumor, hemodinamic instability started and arterial blood pressure and heart rate dramatically increased. Our first reaction was to deepen the anesthesia. Very soon it was obvious that blood pressure increased by the surgeon’s manipulation of the tumor and we started to doubt on catecholamine-secreting tumor. During the course of the operation there were several hypertensive episodes and we managed them by alternately using atenolol, glyceroltrinitrate and anesthetic drug. The patient was extubated 5 hours after transfer to the intensive care unit. Postoperative period was hemodynamically stable. The level of catecholamines in 24-hour urine collection was significantly increased. Pathohistologic diagnosis was mediastinal paraganglioma.