The effect of botulinum toxin A (BTX) was studied on 12 patients with idiopathic craniofacial hyperhidrosis. After confirming the diagnosis by Minor's iodine starch test we first treated one-half of the forehead with an injection of 2.5-4 ng BTX (Dysport) equidistantly intracutaneously. After 4 weeks we assessed the efficacy by another Minor's iodine starch test and then treated the other half. Another 4 weeks later a standardized telephone interview was carried out. After 1-7 days the craniofacial sweating in the area injected had completely ceased in 11 patients and was mildly reduced in the remaining one. The efficacy was confirmed by repeated Minor's iodine starch tests. Mild weakness of frowning was the only side effect, lasting 1-12 weeks and completely resolving in all patients. Although sweating has not yet recurred in most patients at follow-up periods up to 27 months, one patient had a relapse 9 months after treatment. Following reports on palmar and axillary hyperhidrosis and gustatory sweating (Frey's syndrome) this is apparently the first report on the use of BTX in the treatment of idiopathic craniofacial hyperhidrosis. BTX seems a promising new treatment for localized hyperhidrosis.