BACKGROUND: Thoracoscopic sympathectomy seems to be a safe therapeutic procedure without a severe complication. Hypotension has been often reported as one of postoperative complications, but intraoperative changes in blood pressure (BP) were not studied. However, authors' past experience of thoracic sympathectomy told that intraoperative BP reduction could be observed only when measured in ipsilateral arm. During general anesthesia, BP reduction might be a crucial, which could be associated with complication. Authors conducted this study to establish whether BP reduction is confined to ipsilateral arm, or is systemic phenomenon in thoracoscopic sympathectomy. METHODS: Twenty healthy, male and female patients scheduled for one stage thoracoscopic thoracic sympathectomy were prepared for this study. Without premedication, invasive BP monitoring was taken place in bilateral radial arteries. General anesthesia was induced with low dose of fentanyl, propofol and vecuronium. Endotracheal intubation was done with double lumen tube and anesthesia was maintained with variable concentrations of isoflurane in 100% oxygen. Sympathetomies were done for T2~3 during one lung ventilation. BP and palmar temperature were recorded at arrival, after one lung ventilation, after sympathectomy, 5 min, 10 min, after two lung ventilation. BPs and temperatures were analyzed by time and groups. RESULTS: Concurrent with initiation of sympathectomy, BP was reduced only in ipsilateral radial artery. Mean BP decrement was almost 11% (right side: 80 +/- 11 mmHg -> 71 +/- 15 mmHg; left side: 80 +/- 14 mmHg -> 71 +/- 9 mmHg; both of p<0.05). It was accompanied with ipsilateral palmar temperature elevation (right side: 1.28 degrees C; left side: 1.19 degrees C; both of p<0.05). CONCLUSION: Conclusively, BP reduction in thoracic sympathectomy is a change confined to ipsilateral arm, which seems because of peripheral vasodilation.