Context: No randomized trials have been published that address the concern that inhalation of mercury vapor released by amalgam dental restorations causes adverse health effects. Objective: To compare the neuropsychological and renal function of children whose dental caries were restored using amalgam or mercury-free materials. Design and Setting The New England Children’s Amalgam Trial was a 2-group randomized safety trial involving 5 community health dental clinics in oston, Mass, and 1 in Farmington, Me, between September 1997 and March 2005. Participants and Intervention: A total of 534 children aged 6 to 10 years at baseline with no prior amalgam restorations and 2 or more posterior teeth with caries were randomly assigned to receive dental restoration of baseline and incident caries during a 5-year follow-up period using either amalgam (n=267) or resin composite (n =267) materials. Main Outcome Measures: The primary neuropsychological outcome was 5-year change in full-scale IQ scores. Secondary outcomes included tests of memory and visuomotor ability. Renal glomerular function was measured by creatinine-adjusted albumin in urine. Results: Children had a mean of 15 tooth surfaces (median, 14) restored during the 5-year period (range, 0-55). Assignment to the amalgam group was associated with a significantly higher mean urinary mercury level (0.9 vs 0.6 μg/g of creatinine at year 5, P < .001). After adjusting for randomization stratum and other covariates, no statistically significant differences were found between children in the amalgam and composite groups in 5-year change in full-scale IQ score (3.1 vs 2.1, P=.21). The difference in treatment group change scores was 1.0 (95%confidence interval, -0.6 to 2.5) full-scale IQ score point. No statistically significant differences were found for 4-year change in the general memory index (8.1 vs 7.2, P=.34), 4-year change in visuomotor composite (3.8 vs 3.7, P=.93), or year 5 urinary albumin (median, 7.5 vs 7.4 mg/g of creatinine, P=.61). Conclusions: In this study, there were no statistically significant differences in adverse neuropsychologicalor renal effects observed over the 5-year period in children whose caries were restored using dental amalgam or composite materials. Although it is possible that very small IQ effects cannot be ruled out, these findings suggest that the health effects of amalgam restorations in children need not be the basis of treatment decisions when choosing restorative dental materials. Context: No randomized trials have been published that address the concern that inhalation of mercury vapor released by amalgam dental restorations causes adverse health effects. Objective: To compare the neuropsychological and renal function of children who dental caries were restored using amalgam or mercury-free materials Design and Setting The New England Children’s Amalgam Trial was a 2-group randomized safety trial involving 5 community health dental clinics in Boston, Mass, and 1 in Farmington, Me, between September 1997 and March 2005. Participants and Intervention: A total of 534 children aged 6 to 10 years at baseline with no prior amalgam restorations and 2 or more posterior teeth with caries were randomly assigned to receive dental restoration of baseline and incident carsies during a 5-year follow-up period using either amalgam (n = 267 ) or resin composite (n = 267) materials. Main Outcome Measures: The primary neuropsychological outcome was 5-year change in full-scale IQ Secondary outcomes included tests of memory and visuomotor ability. Renal glomerular function was measured by creatinine-adjusted albumin in urine. Results: Children had a mean of 15 tooth surfaces (median, 14) 0-55). Assignment to the amalgam group was associated with a significantly higher mean urinary mercury level (0.9 vs 0.6 μg / g of creatinine at year 5, P <.001). After adjusting for randomization stratum and other covariates, significant differences were found between children in the amalgam and composite groups in 5-year change in full-scale IQ score (3.1 vs 2.1, P = .21). The difference in treatment group change scores was 1.0 (95% confidence interval, - 0.6 to 2.5) full-scale IQ score point. No statistically significant differences were found for 4-year change in the general memory index (8.1 vs 7.2, P = .34), 4-year change in visuomotor composite P = .93), or year 5 urinary albumin (median, 7.5 vs 7.4 m g / gof creatinine, P = .61). Conclusions: In this study, there were no statistically significant differences in adverse neuropsychologicalor renal effects observed over the 5-year period in children whose caries were restored using dental amalgam or composite materials. Although it is possible that very small IQ effects can not be ruled out, these findings suggest that the health effects of amalgam restorations in children need not be the basis of treatment decisions whenorative restorative dental materials.