By careful calculation, a sample size of 382 ADHD subjects will provide adequate power to detect genome-wide significant genetic variations and replicate the findings in an independent validation sample. We anticipate to identify the relationship between genetic variations of ADHD and the endophenotype of spatial working memory. Our findings will significantly contribute to our understanding of the pathophysiological mechanisms of ADHD, especially the pathological pathway from genes, through endophenotype, to behavioral phenotypes.