Objective: This study aimed to examine the influence of dopamine transporter gene (DAT1) 3’UTR genotype on cingulate cortical thickness in a large sample of children and adolescents with ADHD. Method: Brain MRIs were acquired from 46 ADHD patients with homozygosity for the 10-repeat allele and 52 ADHD patients with a single copy or no copy of the allele. The cingulate cortex of each MRI scan was automatically parceled into sulci and gyri as well as into Brodmann areas (BA). Results: There were no group differences in age, gender, full-scale intelligence quotient, symptom severity, treatment status, comorbidity, or mean overall cortical thickness. Sulcus/gyrus- and BA-based analyses revealed that patients homozygous for the 10-repeat allele showed significantly greater thickness in right cingulate gyrus and right BA 24 compared with 9-repeat carriers. Conclusion: These findings suggest that thickness of cingulate cortex is influenced by the presence of the 10-repeat allele in ADHD.