The purpose of this study was to investigate the association between the methylphenidate (MPH) response and the norepinephrine transporter (NET) gene polymorphisms in Korean children with attention deficit hyperactivity disorder (ADHD). One hundred and fourteen children with ADHD (mean age 9.08±1.94 years) were recruited from a child psychiatric clinic in South Korea. The genomic DNA was extracted from the blood lymphocyte. Patients were administered MPH for 8 weeks. Good response was defined as a decrease of more than 50% from the baseline ADHD rating scale-IV scores or Clinical Global Impression-Severity score was 1 or 2 after treatment. We compared the MPH response according to the genotype of G1287A of the NET gene (SLC6A2). In patients with G/G genotype, 41 patients (71.9%) showed good response and 16 patients (28.1%) showed poor response when it was measured by the ADHD rating scale-IV. In comparison, 23 patients (46.0%) with G/A genotype and four patients (57.1%) with A/A genotype showed good response (P=0.018, by the Fisher's exact test). When we compared the response of MPH between patients with G/G genotype and those without G/G genotype, 41 patients (71.9%) with G/G genotype showed good response, whereas only 27 patients (46.4%) without G/G genotype showed good response. [Pearson χ2=7.143, degrees of freedom (df)=1, P=0.008]. Our study found a significant association between the G1287A genotype of the NET gene and the MPH response in Korean children with ADHD. These findings support the significant role of the NET gene in ADHD treatment with MPH.