Background: In attention deficit hyperactivity disorder (ADHD), deteriorations of brain gut axis has been shown in previous studies. One area where the most important challenges are seen in ADHD is social functioning. Zonulin is a protein found in the intestinal intraepithelial component; it has been shown that the level of zonulin increases when intestinal permeability is impaired. Changes in intestinal function were shown in ADHD. Zonulin has been shown to be associated with social impairment in children with autism spectrum disorder. In this study, it was aimed to evaluate the relationship between the ADHD symptoms and zonulin in children with ADHD. Secondarily relation of zonulin and difficulties in social functioning was examined in these children.