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Burgeoning estimates of the prevalence of childhood attention-deficit/hyperactivity disorder (ADHD) raise the possibility of a widespread risk factor. We seek to assess whether artificial food colorings (AFCs) contribute to the behavioral symptomatology of hyperactive syndromes. We searched ten electronic databases for double-blind placebo-controlled trials evaluating the effects of AFCs. Fifteen trials met the primary inclusion criteria. Meta-analytic modeling determined the overall effect size of AFCs on hyperactivity to be 0.283 (95% CI, 0.079 to 0.488), falling to 0.210 (95% CI, 0.007 to 0.414) when the smallest and lowest quality trials were excluded. Trials screening for responsiveness before enrollment demonstrated the greatest effects. Despite indications of publication bias and other limitations, this study is consistent with accumulating evidence that neurobehavioral toxicity may characterize a variety of widely distributed chemicals. Improvement in the identification of responders is required before strong clinical recommendations can be made.