The great majority of the currently available evidence supporting sympathectomy for primary hyperhidrosis is observational, coming from a variety of prospective and restrospective clinical series as well as comparative studies. A cumulative experience in over 6000 patients suggests that ETS is a safe, reproducible, and effective procedure, and most patients are satisfied with the results of the surgery. The currently available experimental data comes from clinical trials that compared alternative levels of sympathetic chain disruption; these trials speak only to the relative merits of one surgical technique over another and do not provide an assessment of the overall impact of surgery in the general population of patients with primary hyperhidrosis. Furthermore, it is difficult to compare series and generalizability is compromised by a lack of uniform definitions and measures at both the exposure and outcome levels. There is marked heterogeneity with respect to study population and entry criteria, with significant variability of site and severity of excess sweating as well as the degree of preoperative conservative management of hyperhidrosis before surgical referral. Also the operative approach varies widely among studies, and the optimal procedure remains elusive: unilateral versus staged nonsimultaneous bilateral versus concomitant bilateral sympathectomy; ganglionic resection versus ablation using electrocoagulation or harmonic scalpel; clipping of the chain to maintain reversibility in the event of intolerable symptoms versus permanent disruption. In addition, the lack of uniform outcome measures makes these data difficult to interpret, and standardized metrics of surgical results are necessary, such as objective quantification of sweating by gravimetry or use of the SF-36 Health Survey Questionnaire as an estimate of patient quality of life. A multicenter, adequately powered, randomized controlled trial comparing surgical to medical management of hyperhidrosis is unlikely given the current enthusiasm for same-day thoracoscopic sympathectomy among surgeons, a largely positive literature replete with encouraging results, and well-informed hyperhidrosis patients who want to be cured of a socially debilitating illness. Future clinical trials in this area will likely compare surgical techniques. For such comparisons, procedures must be standardized and outcome measures validated for both symptoms of the disease and surgical complications. Finally, the studies must have large numbers of patients and adequate long-term follow-up if they are to detect differences in results among procedures with very high technical success rates.