1. The objective of the present study was to compare the phenomenology and pathophysiology of obsessive compulsive disorder (OCD) and attention deficit hyperactivity disorder/deficits in attention, motor control and perception (ADHD/DAMP). 2. Through detailed studies of the literature on OCD and ADHD/DAMP, the phenomenology of these two conditions is compared, and possible underlying pathophysiological mechanisms involving interactions between glutamate, dopamine, serotonin and acetylcholine are discussed, with emphasis on OCD. The present paper also discusses possible mechanisms of action for current pharmacological treatments of OCD and ADHD, as well as possible future treatment strategies for these disorders. 3. OCD and ADHD/DAMP are common neuropsychiatric conditions which in many regards appear to be each other's antipodes with respect to clinical manifestations, associated personality traits and brain biochemistry, notably prefrontal cortical glutamate activity. Future pharmacological treatments of these disorders may involve manipulations with glutamate, dopamine D , serotonin 2A and nicotine receptors. 4. It appears that OCD is a hyperglutamatergic and ADHD a hypoglutamatergic condition, with prefrontal brain regions being especially affected.