Attention deficit hyperactivity disorder (ADHD) is a common neurobehavioral disorder of childhood, affecting approximately 5-10% of children. ADHD is considered to be a multifactorial disorder because both genetic and environmental components may contribute to its progress. The etiology of attention deficit hyperactivity disorder (ADHD) is unknown, however family, twin and adoption studies have suggested that genetic factors are very important in its etiopathogenesis. The research of genetic basis of ADHD consists of linkage analysis, candidate gene approach and association studies. These analyses and also investigations on animal models of disease suggest that mutations in genes involved in dopaminergic, serotonergic and adrenergic systems are likely to be responsible for ADHD.