The dopamine D4 receptor DRD4 gene has been implicated in psychotic, mood, addictive, personality, movement and behavioral disorders [e.g. attention deficit hyperactivity disorder (ADHD)]. Now, there is convincing evidence to support the genetic association of DRD4 polymorphisms with ADHD. The particular polymorphism, a 5′ 120-bp duplication, might be functionally active. These findings suggest that manipulation of the DRD4 gene pathway could offer more selective pharmacological approaches to the treatment of ADHD.