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Children may be at particular risk from toxic effects of mercury (Hg). Previous studies of hair (organic) and urine (inorganic) Hg levels in US children were unable to assess Hg levels while accounting for exposure to amalgam dental restorations. This analysis describes, over a 5-year period, levels and correlates/predictors of scalp hair (H-Hg) and urinary (U-Hg) mercury in 534 New England Children's Amalgam Trial (NECAT) participants, aged 6–10 years and without exposure to dental amalgam at baseline. Results: Mean H-Hg levels were between 0.3 and 0.4 ?g/g over 5 years. 17–29% of children had H-Hg levels 0.5 ?g/g, and 5.0 to 8.5% of children had levels 1 ?g/g, in any given study year. In adjusted models, fish consumption frequency was the most robust predictor of high H-Hg. U-Hg mean levels were between 0.7 and 0.9 ?g/g creatinine over two years. The percentage of those with U-Hg 2.3 ?g/g creatinine ranged from 4% to 6%. Number of amalgam restorations had a significant dose-response relationship with U-Hg level. Daily gum chewing in the presence of amalgam was associated with high U-Hg.