The clinical spectrum of sweating disorders includes sudomotor excess and deficiency. Hyperhidrosis is characterized by sweating beyond that required to maintain a constant internal body temperature. Hypohidrosis and anhidrosis are distinguished by a reduced or absent ability to generate sweat for the purpose of evaporative heat dissipation. Whereas hyperhidrosis is usually benign, anhidrosis may predispose to hyperthermia. Either hyperhidrosis or anhidrosis may accompany a more serious underlying disorder. Correct diagnosis depends on determining the anatomical pattern of sweating and localizing the lesion within the autonomic nervous system. Sudomotor deficits may involve the frontal operculum, hypothalamus, brain stem, spinal cord, sympathetic chain ganglia, peripheral nerve, or eccrine sweat glands. Treatments for hyperhidrosis include topical aluminum chloride, oral anticholinergic agents, intradermal botulinum toxin for some localized syndromes, and thoracic ganglionic sympathotomy or sympathectomy for refractory palmar hyperhidrosis.