Botulinum toxin (BTx) is an important therapeutic agent with widespread applications in neurologic and non-neurologic disease. One of the most potent neurotoxins known, BTx derives its name from the Latin word for sausage, botulus— referring to poisoning from badly prepared meat in the early 19th century. The toxin is a 150-kDa protein produced by Clostridium botulinum and composed of a heavy and light chain linked by a disulfide bond. When activated, the toxin targets peripheral cholinergic systems and prevents the release of acetylcholine. The heavy chain mediates binding to presynaptic cholinergic nerve terminals and internalization of the toxin into the cell. The light chain is a zinc endopeptidase responsible for its toxic effects and cleaves specific proteins needed for synaptic transmission (1). The first therapeutic use of BTx, purified and highly diluted, was as a treatment for strabismus in the 1970s (2). Seven serotypes of BTx have been identified, each with a specific mode of action at the molecular level. Currently, serotypes A (Botox [Allergan, Inc., Irvine, California]; Dysport [Ipsen, Ltd., Berkshire, England]) and B (Myobloc [Solstice Neurosciences, Inc., South San Francisco, California]) are available for clinical use. Over the past 25 years, BTx has proved to be remarkably successful in relieving spasms, unwanted movements, abnormal postures, and pain associated with many disorders (1).