Objectives : The aim of this study was to investigate the association between Korean ADHD patients and the l/s polymorphism of serotonin transporter(5-HTTLPR). Methods : The study sample consisted of 189 Korean ADHD children diagnosed by Kiddie-Schedule for Affective Disorders and Schizophrenia-Present and Lifetime Version-Korean Version(K-SADS-PL), both parents of ADHD children, and 150 normal children. DNA were extracted from the blood of all samples, and genotyping was done. Based on the allele and genotype information, not only the case-control analysis between ADHD and normal children but also the family-based association test among ADHD children and their parents. Transmission disequilibrium test(TDT) were performed for family-based associated test(number of trio=113). The results of the clinical rating and neuropsychological tests were compared according to the l/s genotype of ADHD children. Results : In case-control analysis, there were no statistically significant difference of l/s gene polymorphism between ADHD and normal children in various kinds of analysis condition. In family-based association study, TDT failed to detect linkage disequilibrium between l/s gene polymorphism and ADHD in whole ADHD families. However, in the families of ADHD inattentive type only(number of trio=23), I allele was transmitted more preferentially in the proband with ADHD even if the number of families was small(${chi}^2$=4.57, p=.032). In the analysis of the results from the clinical scales and neuropsychological tests in ADHD children, the score of the Novelty- Seeking of ADHD children with l/l genotype was significantly lower than with the other genotypes(F=3.15, p=.047), and that of Self Transcendence was significantly higher(F=4.25, p=.017). Conclusion : The results of this study suggest there were no significant genetic association between the 5- HTTLPR gene polymorphism and Korean ADHD.