Dental amalgam—a mixture of elemental mercury and a silver-dominated metal alloy—has been the most widely used dental filling material for well over a century. Alternative materials exist but are not well suited for some important applications, and all are more expensive than amalgam. The toxic effects of occupational mercury exposure have long been known, but it was not until about 1980 that serious consideration was given to the possibility that mercury vapor escaping from amalgam fillings might be affecting health, specifically producing subtle effects on the central nervous system. Such effects have been reported among dentists and other dental personnel, whose exposures are well below industrial levels but above those from fillings alone. No large studies have been completed that examine the effects of mercury exposure from dental amalgam fillings. In the face of inadequate evidence on the possible risks of dental amalgam, countries have reacted disparately. Sweden is phasing out amalgam entirely, possibly by the end of 1997. Germany has produced guidelines for limiting its use, other countries have signaled their intention to reduce it, and others—the United States and Canada—have studied the matter but taken no action. Policy differences within Europe have made dental amalgam a test case for the European Community's new medical device regulations. Relatively little epidemiologic research has been initiated to try to answer the question of dental amalgam's possible health effects. An international effort to define and carry out a research agenda to guide public policy is called for.