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Objective: Attention deficit hyperactivity disorder (ADHD) is quite common in the general pediatric population. In this population, sympathomimetic drugs, which are at risk of arrhythmia, are frequently used. In this study, ECG characteristics of drug naive ADHD patients were compared control group. Methods: This study was performed 43 drug naive ADHD patients and 36 healthy children who admitted to the child and adolescent psychiatry outpatient clinic between November 2017 and January 2018. A standard 12-lead ECG of the patient and control group were evaluated. The ADHD and control group data were compared by calculating the minimum and maximum QT inter-val, corrected QT (QTc), QT dispersion (QTd), the peak and the end of the T wave (Tp-e) and Tp-e dispersion (Tp-ed) on 12-lead surface ECG. Tp-e interval was measured tangent method. The Bazett formula was used for QT correction. Results: The mean age of the patients with ADHD was 10.6±3.2 and 62.8% of them were male and similar to the control group. There was no significant difference between ADHD and control groups in terms of heart rate, min QT, max QT and min Tp-e values. QTc, QTd, max Tp-e and Tp-ed intervals were statistically higher ADHD patients than control group. Conclusion: QT dispersion and Tpe is a measure of transmural dispersion of repolari-zation and related to cardiac arrhythmias. High QTd, QTc, max Tp-e and Tp-ed intervals in ADHD patients may indicate a potential cardiac arrhythmia. Physicians should make careful assessments of ADHD patients before pre-scribing sympathomimetic drugs. [Anadolu Psikiyatri Derg 2018; 19(6.000): 624-630]