Essential palmar hyperhidrosis is a disease characterized by excessive sweating on palms and hands due to hyperaction of sympathetic nervous discharge. It develops severe hypothermia on both hands because of loss of surface heat by evaporation of the sweating. Numerous tests including starch-iodine test were used to detect sweating status. But they were complicated and unpleasant to patients. Digital infrared Thermographic Imaging(DITI) can show a thermal difference very clearly. We have used DITI not only for the diagnosis, but for planning of the operation and operative follow up of the disease since 1990. 343 cases of bilateral upper thoracic(T2 & T3) sympathetic ganglionectomy were performed from Mar. 1989 to Dec. 1996 in our spine center. Among them, open surgery with posterior midline approach were initially carried out in 54 cases and recently percutaneous endoscopic sympathectomy were carried out in 289 additional cases. Digital Infrared Thermographic Imaging has been taken pre and postoperatively in 339 cases. Preoperatively, severe hypothermia is noted in 96.2% in both hands and feet. Immediately after operation, the sweating ceased in all cases and marked hyperthermia was noted in both hands compared to preoperative status due to sympathetic denervation. DITI is more accurate and easier than any other method for diagnosis and evaluation of treatment effect in hyperhidrosis. DITI is simple, accurate, comfortable and objective diagnostic tool for hyperhidrosis patient.