Botulinum toxin A is widely used in Europe and the USA for the treatment of localized hyperhidrosis, and its efficacy has been recognized. In this study, botulinum toxin A (Botox) was locally injected at 30 sites (2 U/injection) on the right palm in 27 patients with palmar hyperhidrosis (14 severe patients, 13 mild patients), and the results confirmed the efficacy of injection. The amount of sweat was then quantified for the left and right hands every month after local injection. The quantity of sweat on the treated hand was approximately one-fifth that on the untreated hand. In addition, the quantity of sweat on the untreated hand decreased slightly. Over time, the quantity of sweat on the treated hand increased slightly, but the quantity of sweat on the treated hand at 6 months after injection was less than half that before injection, and there were significant differences before and after injection. In the present study, severe sweating was defined as 1 mg/cm2/min or more and mild sweating as less than 1 mg/cm2/min, and the therapeutic effects of botulinum toxin A were analyzed in relation to severity. When compared to the mild cases, the quantity of sweat remained higher in the severe cases after botulinum toxin A therapy. Therefore, to achieve satisfactory effects in severe cases, it would be necessary to increase the number of injection sites, as well as injection dose.