Hyperhidrosis is a clinical condition defined as abnormal perspiration, in excess of that required for regulation of body temperature. It can be generalised or localised (the most frequently affected areas are the armpits, palms of the hands, soles of the feet and the groin area), and can be congenital or acquired, primary or secondary. Congenital hyperhidrosis appears to be connected to an autosomal dominant genetic disfunction; it usually begins in or shortly before adolescence. Acquired hyperhidrosis, on the other hand, is often a manifestation of pathologies or systemic conditions (e.g. diabetes, thyroid disfunction etc.). Treatment with oral anticholinergic drugs is very effective but incurs important side effects, such as drowsiness and extreme dryness of the eyes and mouth. Suggested surgical treatments are removal of the glandular tissue or thoracic sympathectomy. These procedures also often incur side effects and are indicated only for the most serious cases. Injection with botulinum toxin is the therapy that is best tolerated, and has a very high satisfaction rate. This paralyses the cholinergic muscles around the sweat glands, and completely eliminates perspiration. The results are long-lasting and have profound positive impact on patients’ social lives.