Objective: Palmar hyperhidrosis can be psychosocially devastating. Sympathectomy provides effective treatment. The most common side effect after sympathectomy is compensatory hyperhidrosis, which can be debilitating. Controversy exists as to which and how many levels treated carry the lowest incidence of compensatory hyperhidrosis after sympathectomy for palmar hyperhidrosis. Methods: Retrospective review was conducted on a video-assisted thoracoscopic surgical database including all patients who underwent video-assisted thoracoscopic surgical sympathectomy for palmar hyperhidrosis. Results: Video-assisted sympathectomy was performed in 282 patients for palmar hyperhidrosis from May 2002 through July 2005; in all, 179 patients (64%) underwent division at T2 level only and 103 at levels T2, T3, and T4. The groups were similar in age and sex distribution. The rate of compensatory hyperhidrosis was significantly less in the T2 group (23 patients, 13%) than in the T2 through T4 group (35 patients, 34%)(P = .011). The most common site of compensatory hyperhidrosis in both groups was the lower back. Patients with compensatory hyperhidrosis were older (median 31 years vs 23 years, P = .037), had body mass index greater than 28 (P = .048), and underwent multiple level sympathectomy (P = .004). Conclusion: Compensatory hyperhidrosis continues to occur after sympathectomy for palmar hyperhidrosis; however, a significant reduction in incidence can be achieved by dividing the sympathetic chain at a single level (T2). Patients who are older and/or have increased body mass index should be warned of their increased risk of compensatory hyperhidrosis after sympathectomy. © 2009 The American Association for Thoracic Surgery.