Abstract: Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable neuro developmental disorder. Traditionally ADHD was considered a childhood disorder but recent evidence confirms that ADHD can also occur in adulthood. The prevalence of ADHD worldwide is around 5% in children and 3% in adults. ADHD affects patients throughout their lives by causing failures in education as well as in occupations, which increase the risk of accidents and criminality. The disorder has no single cause, which reflects the heterogeneity of ADHD. Understanding the genetic and molecular changes associated with familial/heritable ADHD development is challenging, due to the lack of relevant models of ADHD and the difficulty of collecting brain samples. The current review will highlight upon the genetic diversity of ADHD and summarize some recent relevant studies. Knowledge about the ADHD’s variants might be useful for a new ADHD genetic research.