Background: This study aimed to evaluate the clinical efficacy and safety of endoscopic thoracic sympathicotomy and to explore strategies to decrease the incidence of transfer hyperhidrosis (TH). Methods: From January 2003 to July 2016,10,275 patients with primary palmar hyperhidrosis underwent endoscopic thoracic sympathicotomy in 15 different institutions. We carried out a retrospective analysis of these patients who were grouped into group A, those with nonretained R2 (R2, R2-3, or R2-4 ablation), and group B, those with retained R2 (single R3 or R4 ablation). Results: All procedures were performed successfully. Both hands of all patients became warm and dry immediately after endoscopic thoracic sympathicotomy. Pneumothorax occurred in 146 patients, and 39 patients had intraoperative bleeding. Follow-up was carried out from 6 months to 13 years. A total of 531 patients (5.2%) were lost to follow-up. The effective rate for primary palmar hyperhidrosis was 100%. Palmar hyperhidrosis recurred in 73 patients (0.7%). Transfer hyperhidrosis appeared in 7,678 patients (78.8%). For groups A and B, the incidence of TH was 80.4% and 78.5%, respectively (P > .05), but the incidence of grade III+IV TH in group B (1.6%) was less than that in group A (4.8%; P < .001). Conclusion: Endoscopic thoracic sympathicotomy is a minimally invasive, safe, and effective therapeutic method for primary palmar hyperhidrosis. Although the overall incidence of TH is high, the incidence of grade III to IV TH can be decreased by reserving R2, lowering the level of thoracic sympathicotomy, and single severing of R3 or R4. (C) 2019 Elsevier Inc. All rights reserved.