Background: Thoracic T_2–4 sympathectomy (TS) relieves palmar hyperhidrosis. These same roots innervate the heart and the lung. Thoracoscopic TS minimizes damage to the chest wall so that the effect of sympathectomy itself on these organs can be studied. We attempted to determine whether attenuated sympathetic output affects arm or leg exercise tolerance and lung function in young adults who underwent this operation. Methods: Seven subjects, aged 17–30 years, had lung function tests (water spirometer, Godart, Holland), and leg and arm maximal exercise (CPX, MedGraphics, USA), before and 3–6 months after TS. Results: After TS, resting and exercise heart rate and blood pressure were reduced. Baseline leg and arm peak O₂ uptake, 2.08 (0.6) and 1.44 (0.5) liters/min, respectively, were not different from the post-TS values, 2.06 (0.7) and 1.54 (0.5) liters/min (nonsignificant). Post-TS lung functions were not significantly reduced. Conclusion: Thoracoscopic T_2–4 sympathectomy does not lead to a clinically important fall in lung function and does not compromise arm or leg exercise capacity. Therefore, TS can be done safely in young subjects with palmar hyperhidrosis.