The comorbidity between obsessive-compulsive disorder (OCD) and attention deficit/hyperactivity disorder (ADHD) has been discussed for a couple of decades. Reported co-occurrence rates are highly inconsistent in the literature.

To review phenomenological and theoretical issues concerning concomitant OCD-ADHD.

Phenomenological and theoretical issues regarding OCD-ADHD comorbidity are reviewed.

Although numerous studies suggest an OCD-ADHD comorbidity, thus far etiological (i.e., genetic) background has been provided only for a pediatric comorbidity. High rates of co-occurrence may be mediated by the existence of tic disorders, and evidence of impaired neuronal maturational processes in OCD pediatric population may lead to probably transitory phenotypical expressions that look like ADHD symptomatology. Thus, it is possible that ADHD-like symptoms resulting from OCD-specific symptomatology may be misdiagnosed as ADHD. This may explain the lower co-occurrence rates reported in adolescents and adults.

OCD and ADHD are very different disorders in terms of pathophysiology, phenomenology, and treatment strategies. Several methodological concerns have been identified in our review. Future studies on OCD-ADHD comorbidity should try to mitigate these biases.

The authors have not supplied their declaration of competing interest.