There is an association between bruxism and ADHD. No published data on psychiatric comorbidities in attention-deficit/hyperactivity disorder (ADHD) children with bruxism were found. There is no satisfying treatment method for children with bruxism. If we understand its comorbidities well, a better treatment method could come out. This study was conducted to compare the frequency of comorbid psychiatric disorders in the parents and their ADHD children with and without teeth grinding. It was hypothesized that there is no association between bruxism and prevalence of comorbid psychiatric disorders in children with ADHD and their parental psychopathology. Eighty-nine ADHD children without teeth grinding were compared with 32 ADHD children with teeth grinding. Their parental psychiatric disorders were also compared. Structured interviews were used to diagnose comorbid psychiatric disorders. The demographic characteristics of the children and their parents were not different between the groups. The only psychiatric disorder in children, which was associated with the groups was oppositional defiant disorder. The rate of conduct disorder, tic disorder, major depressive disorder, separation anxiety disorder, generalized anxiety disorder, enuresis, and obsessive compulsive disorder were not different between the two groups of children. The rate of major depression was more in the mothers of children with teeth grinding than those without such children. These finding were not reported before. ADHD children with teeth grinding have a high prevalence of oppositional defiant disorder. Lack of association between anxiety disorder and presence of teeth grinding might not support the idea that anxiety is associated with teeth grinding. The association of ODD and teeth girding might be a clue about etiology of bruxism. Perhaps, this clue can probably lead to the development of a more satisfying treatment. With consideration of this clue, further studies should survey if there is any association between ODD and sleep micro-arousals.