Mercury has been used for centuries for medical, chemical, metallurgical and electrical applications. It is an element of mystery, which in its metallic form is an enticing silvery liquid that can be as fascinating as it is dangerous. Its use in dental amalgam has a potential for continuous occupational exposure of dental practitioners to mercury vapor. It is imperative that the dental practitioner understands the hazards associated with the use of mercury, and controls exposures to prevent the development of any untoward effects. This article provides an overview of the toxicology of the different forms of mercury to which human exposure occurs and addresses safety issues associated with mercury vapor, the primary form of mercury encountered in the practice of dentistry.