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Background: Drug treatment is one of the most important treatments for attention deficit hyperactivity disorder (ADHD). The DRD4 gene is a transporter and receptor coding gene of dopamine and is one of the most important genes under investigation in the disorder and etiology of ADHD. In this study, the association between rs3758653 C/T and VNTR exon 3 repetition polymorphisms of the DRD4 gene and the effects of methylphenidate were investigated in patients with ADHD disorder consuming methylphenidate. Methods: The descriptive-analytical study was performed on 122 patients (5 - 18 years old) with ADHD who were treated with methylphenidate. DNA was extracted using salting out method. Subsequently, the rs3758653 polymorphism in the 5'UTR region of DRD4 gene was genotyped by PCR-RFLP method, and the VNTR fragment in exon III of DRD4 gene was investigated by electrophoresis gel on acrylamide gel method. After eight weeks from the start of drug treatment with methylphenidate, the intensity of symptoms was evaluated using the Conners scale. Finally, all data from questionnaires and information that were resulted from laboratory findings were analyzed using ANOVA and repeated measure analysis. Results: Of the 122 patients under study, 15 patients (12.3%) were responded to the drug treatment, and 107 patients (87.7%) were not responded. The significant differences were not revealed in genotype, and allele frequencies of between rs3758653 (C/T) and exon III 3'VNTR repeats polymorphisms of the DRD4 gene and responder and non-responder of ADHD groups to the drug treatment. Conclusions: The results showed that the reduction of ADHD symptoms with drug treatment is not related to DRD4 sub-types in patients with ADHD.