Botulinum toxin has the ability to block cholinergic nerve transmission to skeletal muscle and thus produce a temporary flaccid paralysis. This has enabled physicians to treat a number of medical problems characterized by hyperfunctional muscle. This has also enabled cosmetic physicians to soften or eliminate rhytides caused by hyperfunctional muscles. A thorough understanding of the muscular anatomy of the face is necessary for the judicious use of botulinum toxin (Appendix 4).