The placement of mercury-containing dental fillings during pregnancy did not result in an increased risk of a low-birth-weight infant. While a weak dose-response trend was observed for term low-birth-weight infants, both the small size of the risk increase and the width of the confidence intervals precluded making any meaningful inferences, and associations were not identified between restorative dental procedures, regardless of chemical composition, and birth weight. These findings do not provide support to the hypothesis that mercury-containing dental amalgams placed during pregnancy affect birth weight. Potential reasons for the absence of an association include the low dose of inorganic mercury exposure associated with dental filling placement during pregnancy, the absence of organic mercury in dental filling materials, and the true absence of a biologic mechanism by which elemental mercury affects birth weight.