Abstract： Background Compensatory sweating (CS) is one of the most common postoperative complications after thoracic sympathectomy, sympathicotomy or endoscopic sympathetic block (ESB) for palmar hyperhidrosis. This study was conducted to examine the relevance between CS and the sympathetic segment being transected in the surgical treatment of palmar hyperhidrosis, and thus to detect the potential mechanism of the occurrence of CS.Methods Between October 2004 and June 2006, 163 patients with primary hyperhidrosis were randomly divided into two groups, T3 sympathicotomy (78 patients) and T4 sympathicotomy(85), who were operated upon under general anesthesia via single lumen intubation and intercostal video-mediastinoscopy (VM).Results No morbidity or mortality occurred. Palmar hyperhidrosis was cured in all patients. Follow-up(mean (13.8±6.2)months) showed no recurrence of palmar hyperhidrosis. The difference of rates of mild CS in groups T3 and T4 was of no statistical significance. The rate of moderate CS was significantly lower in group T4 than in group T3. No severe CS occurred.Conclusion The rates of occurrence and severity of CS are lowered with the lower sympathetic chain being transected.