Objective: The study aimed to investigate whether the fine motor skills measured by the Functional Dexterity Test (FDT) in ADHD children differ from healthy controls. The second aim was to assess the applicability of the FDT assessment method among ADHD children. Method: The FDT results as an objective assessment of hand skills were compared between 7 and 17 years old ADHD cases (n = 146) and age and gender-matched healthy controls (n = 213). Results: We found lower dominant and non-dominant processing time (respectively for dominant hand and non-dominant hand p = .001, effect size Cliff's Delta = .22; p = .001, ES Cliff's Delta = .29), higher peg processing speed (p = .001, ES Cliff's Delta = .23; p = .001, ES Cliff's Delta = .29), higher total error (p = .001, ES Cliff's Delta = .40; p = .001, ES Cliff's Delta = .51), and total FDT time (p = .0017, ES Cliff's Delta = .14; p = .011, ES Cliff's Delta = .16) in ADHD patients compared to healthy controls. Conclusion: Manual dexterity evaluation would be helpful to detect the fine motor skill deficits of ADHD children. Although ADHD children were advantageous regarding speed, they were disadvantageous regarding processing errors and total process time. Therefore, the error time data should be considered in evaluating ADHD children, unlike healthy children.