Attention deficit hyperactivity disorder (ADHD), characterized by inattention, hyperactivity and impulsivity, is an early onset, highly heritable, clinically heterogeneous, long-term impairing disorder with tremendous impact on individuals, families, and societies. Our research team has conducted a series of biological studies on spatial working memory deficits of ADHD, and substantial evidence has suggested spatial working memory deficits as the important neuropsychological biomarker with translational values and favorable endophenotypic properties for ADHD. Despite the abundance of molecular genetic studies on ADHD, the genetic etiologies of ADHD have been non-conclusive. Because genetic studies on endophenotypes can offer more information on genetic and brain process, endophenotypic approach can efficiently enhance the statistical power and make genome-wide association studies (GWAS) applicable in much smaller sample. To date, there has been no GWAS study on spatial working memory deficits of ADHD.