Excessive axillary hyperhidrosis is a socially embarrassing condition which severely reduces quality of life and may result in psychological disturbance. Available treatment strategies do not resolve the problem in all cases. Intracutaneous injections of botulinum A toxin have been shown to be effective in patients with local sweating disorders. We performed a randomized, double-blind, within-group comparison in 13 individuals (nine women and four men) with severe axillary hyperhidrosis resistant to conventional treatment, to study the effect of intracutaneous injections of botulinum toxin on sweating. A total dose of 200 mouse units of botulinum A toxin (Dysport®) was injected into six different sites in one axilla, 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 difference in ninhydrin staining between botulinum-treated and placebo-treated axillae was −34.5% (P < 0.001), after 8 weeks −36.9% (P < 0.001) and after 13 weeks −28.4% (P < 0.001). Subjective rating of sweat production was evaluated on a visual analogue scale (0, no sweating, to 100, most severe sweating). Three weeks after treatment the difference between the botulinum-treated and placebo-treated axillae was −56.5% (P < 0.001), after 8 weeks −67.4% (P < 0.001) and after 13 weeks −62.5% (P < 0.001). No serious side-effects were observed.