OBJECTIVE: To characterize the relationship between IQ and attention deficits in children with ADHD and to estimate the inattention-related mean influence on IQ when children are tested before stimulant drug treatment has been initiated. METHOD: Studies of various methodologies are reviewed. RESULTS: Correlation studies show mostly weak associations between IQ scores and attention deficits. Meta-analyses report the average short-term stimulant treatment effect on IQ in children with ADHD to be 2 to 7 IQ points. CONCLUSION: The associations between IQ and attention deficits in ADHD are generally modest, with the mean influence on IQ probably amounting to 2 to 5 IQ points. This may serve as a benchmark when clinicians interpret the validity of IQ in this clinical population.