This study compares the results obtained of video-assisted sympathectomy performed on two distinct ganglion levels (third vs. fourth thoracic ganglion) in the treatment of palmar hyperhidrosis (PH), through a blind randomized clinical trial. All participants were randomized into two groups of 20 patients (G3 and G4) and underwent the operation, and were followed for 12 months. We used an objective method for measuring sweat, checking the transepidermal water loss (TEWL), and evaluated the quality-of-life (QoL) before and after the operation. All patients (n=40) ceased suffering from PH after surgery, with statistical difference when we compared the values of TEWL palmar preoperatively with their respective values at one week, one month, six months and 12 months. The main side effect observed was compensatory hyperhidrosis (CH), which was most frequent in G3 after 12 months of follow-up. There was an improvement in QoL since the first evaluation of the postoperative period with no difference between groups. Both techniques were effective in the treatment of PH, generating objective reduction of TEWL regardless of the ganglion operated. Sympathectomy G3 had a higher incidence of CH, yet the improvement in QoL was similar in both groups.