The most poisonous substance known to man, botulinum toxin has successfully established itself as a therapeutic agent over the years. Initially used to treat strabismus, botulinum toxin is now an accepted treatment in a wide spectrum of disorders and has over a 100 potential medical applications. The somewhat loosely-applied term 'wonder drug' could not be better employed to describe the remedial potential of this agent. With time, and through further studies, it is likely that the number of conditions treated with botulinum toxin will keep expanding. This review will focus on the mechanisms of action of botulinum toxin and the evidence behind its use in a variety of conditions.