The aim of this study was to evaluate the learning curve of upper dorsal thoracoscopic sympathectomy. From June 1993 to December 1996, we performed 232 sympathectomies on 116 patients with primary palmar hyperhidrosis. The T2-T3 ganglia were resected by electrocuting and were removed for histologic examination. The series was divided into two groups of 58 patients each, and operations in each group occurred during a period of 21 months. Follow-up was obtained on 111 patients for a mean of 25.06 ± 12.62 months. All limbs were dry after the operation, and hyperhidrosis did not recur. The anesthesia time was reduced, but the operating time, the difficulty in identifying and in resecting the ganglia, compensatory hyperhidrosis, postoperative neuralgia, and subjective satisfaction with the procedure were similar in both groups. The learning curve in the present study was mainly reflected by a reduction in the incidence of Horner's syndrome.