We performed a randomized double-blind study within-group comparison in 11 patients to study the effect of subcutaneous injections of botulinum A toxin in focal hyperhidrosis of the palms. A total dose of 120 mU (mouse units) of botulinum A toxin (Dysport) was injected into six different sites on one palm, whereas the other was injected with sterile saline. Objective quantification of sweat production was performed using digitized ninhydrin-stained sheets. Three weeks after treatment, the mean reduction of sweat production in the botulinum A toxin-treated palms was 26% (P < 0.001), after 8 weeks 26% (P = 0.002) and after 13 weeks 31% (P < 0.001). Subjective assessment of sweat production by the patients using a visual analogue scale showed a 38% improvement in the botulinum A toxin-treated palms at 3 weeks (P = 0.002), 40% at 8 weeks (P = 0.002) and 38% at 13 weeks (P = 0.002). Neither the objective measurement nor the subjective rating showed a statistically significant reduction of sweating in the placebo-treated palms. Three patients reported reversible minor weakness of powerful handgrip after injection at the toxin-treated site, lasting between 2 and 5 weeks.