Patients with attention deficit hyperactivity disorder(ADHD) have symptoms of inattention, hyperactivity, impulsivity. Symptoms of ADHD are responsive to medications such as methylphenidate, dextroamphetamine, pemoline, and bupropion. The functional change of the dopamine transporter is related to the therapeutic effect of these drugs. This can be one reason for the dopamine transporter to be emphasized in the research field of ADHD. ADHD has a genetic tendency. Since dopamine transporter gene(DAT1) knock out mice were reported to be several times more active than normal mice in a novel situation, lights has been shed on DAT1 as a candidate gene for ADHD. Though there have been several studies which reported an association between DAT1 and ADHD, the association between DAT1 and ADHD is not conclusive. Since Vandenbergh reported the DAT1 polymorphism with variable number of tandem repeats(VNTR), and the racial differences in allelic frequencies of the DAT1, wide ethnic variation in the distribution of the DAT1 polymorphism had been confirmed. Wide ethnic variation in the distribution of the DAT1 suggested that there might be ethnic difference in the association between DAT1 and ADHD. Before applying previous findings to Koreans, verification might be needed for Korean patients with ADHD.